Exam Two Flashcards by Khadeeja Ali

Your car moves at constant velocity down the street. What is the magnitude of
the net force?
(A) Fnet> 0
(B) Fnet=0
(C) Fnet<0

(B) Fnet=0

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The horizontal surface on which
the block slides is frictionless. If
the two forces acting on it each
have magnitude F = 30 N and
M = 10 kg, what is the
magnitude of the resulting
acceleration of the block?

(A)3 m/s2
(B)5.6 m/s2
(C) 6 m/s2
(D)7.3 m/s2
(E)8.2 m/s2

6 m/s2

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An 80 kg passenger in
an SUV traveling at 100
km/h is wearing a seat
belt. The driver slams on
the brakes and the SUV
stops in 45.0 m. Find the
force of the seat belt on
the passenger.
(A) 352 N
(B) 496 N
(C) 688 N
(D) 800 N
(E) 904 N

688

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Two blocks are at rest and in
contact on a frictionless
surface as shown below, with
m1=2kgandm2 =6kg
and applied force F = 24 N.

(a) Find the acceleration of the
system of blocks. (b) What is
the force the m2 feels?

acceleration–> 3m/s2
force–>18N

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A truck collides with a car, and during
the collision, the net force on each
vehicle is essentially the force exerted
by the other. Suppose the mass of the
car is 550 kg, the mass of the truck is
2200 kg, and the magnitude of the
truck’s acceleration is 10 m/s2. Find
the magnitude of the car’s
acceleration.
(A) 20 m/s2
(B) 30 m/s2
(C) 40 m/s2
(D) 50 m/s2
(E) 60 m/s2

40 m/s2

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two forces of F1=2.5i+j and F2=-i-1.5j act on an object.Find the third force F3 that is needed to balace the first two forces.

F3=-1.5i+0.5j

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The rocket sled shown below accelerates opposite to the motion at a rate of 196 m/s2. What force is necessary to produce this acce;eration opposite to the motion? Assume that the rockets are off. The mass of the system is 2.1 x10^3 kg.

4.12×10^5
N in the opposite direction of the motion

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suppose two children push horizontally but in exactly opposite direction on a third child in a wagon. The first child exerts a force of 75 N the second exerts a force of 90 N friction is 12 N and the mass of the third child plus wagon is 23 kg. (a.) what is the system of interest if the acceleration of the child in the wagon is to be calcuated? (b.) calculate the acceleration (d) what would the acceleration be if fricion were 15 N?

(a.) child two 90 N
(b.)0.13
(c.)0

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a rocket sled accelerates at a rate of 49 m/s2.Its passenger has a mass of 75 kg. (a.) calculate the horizontal component of the seat exerts against his body.compare this with his weight using a ratio.(b.) calcucate the direction and magnitude of the total force the seat exerts against hus body.

(a) Horizontal Force: 3675 N
Comparison with Weight: Ratio is approximately 5:1
(b) Total Force: 3747 N at an angle of 11.3° above the horizontal

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(a.) find an equation to determine the magnitude of the net force required to stop a car of mass,m, given that the intial speed of the car and the stopping distance is x(b.) find the magnitude of the net force if the mass of the car is 1050 kg the intial speed is 40 km/h and the stopping distance us 25 m.

(a) Fnet= mv^2/2x
(b) The magnitude of the net force is approximately 2593 N.

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a bird has a mass of 26 g and perches in the middle of a streched telephone line. (a) show that the tension in the line can be calcuated using the equations T=mg/2sin(theta). Determine the tension when (b.) theta=5 (c.) theta=0.5.Assume that each half of the line is straight

(a.) T=mg/2sin(theta)
(b.) T=1.46
(c.) T=14.55

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A 2.0 kg block is on a perfectly smooth ramp that makes an angle 30 of with the horizontal (a.) what is the block’s acceleration down the ramp and the force of the ramp on the block (b.) what force applied upward along and parallel to the ramp would allow the bloick to move with constant velocity?

(a)
Acceleration down the ramp: 4.905 m/s²
Normal force: 16.98 N
(b)
Force to move with constant velocity: 9.81 N

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Problem:

A 20 kg crate is placed on the floor of an elevator. The elevator is accelerating upward at 1.5 \, \text{m/s}^2. What is the magnitude of the normal force exerted by the elevator floor on the crate?

A) 176 N
B) 196 N
C) 226 N
D) 166 N

226

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Two ropes are attached to a tree, and forces of F⃗ 1=2.0iˆ+4.0jˆN
and F⃗ 2=3.0iˆ+6.0jˆN
are applied. The forces are coplanar (in the same plane). (a) What is the resultant (net force) of these two force vectors? (b) Find the magnitude and direction of this net force.

a. F⃗ net=5.0iˆ+10.0jˆN
; b. the magnitude is Fnet=11N
, and the direction is θ=63°

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Two teenagers are pulling on ropes attached to a tree. The angle between the ropes is 30.0°
. David pulls with a force of 400.0 N and Stephanie pulls with a force of 300.0 N. (a) Find the component form of the net force. (b) Find the magnitude of the resultant (net) force on the tree and the angle it makes with David’s rope.

a. F⃗ net=660.0iˆ+150.0jˆN
; b. Fnet=676.6N
at θ=12.8°
from David’s rope

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While sliding a couch across a floor, Andrea and Jennifer exert forces F⃗ A
and F⃗ J
on the couch. Andrea’s force is due north with a magnitude of 130.0 N and Jennifer’s force is 32°
east of north with a magnitude of 180.0 N. (a) Find the net force in component form. (b) Find the magnitude and direction of the net force. (c) If Andrea and Jennifer’s housemates, David and Stephanie, disagree with the move and want to prevent its relocation, with what combined force F⃗ DS
should they push so that the couch does not move?

a. F⃗ net=95.0iˆ+283jˆN
; b. 299 N at 71°
north of east; c. F⃗ DS=−(95.0iˆ+283jˆ)N

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Astronauts in orbit are apparently weightless. This means that a clever method of measuring the mass of astronauts is needed to monitor their mass gains or losses, and adjust their diet. One way to do this is to exert a known force on an astronaut and measure the acceleration produced. Suppose a net external force of 50.0 N is exerted, and an astronaut’s acceleration is measured to be 0.893m/s2
. (a) Calculate her mass.

m=56

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The rocket sled shown below accelerates opposite to the motion at a rate of 196m/s2
. What force is necessary to produce this acceleration opposite to the motion? Assume that the rockets are off. The mass of the system is 2.10×103
kg.

Fnet=4.12×105N

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What is the acceleration opposite to the motion of the rocket sled if it comes to rest in 1.10 s from a speed of 1000.0 km/h? (Such acceleration opposite to the motion caused one test subject to black out and have temporary blindness.)

a=253m/s2

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A powerful motorcycle can produce an acceleration of 3.50m/s2
while traveling at 90.0 km/h. At that speed, the forces resisting motion, including friction and air resistance, total 400.0 N. (Air resistance is analogous to air friction. It always opposes the motion of an object.) What is the magnitude of the force that motorcycle exerts backward on the ground to produce its acceleration if the mass of the motorcycle with rider is 245 kg?

Fnet=F−f=ma⇒F=1.26×103N

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The driver in the previous problem applies the brakes when the car is moving at 90.0 km/h, and the car comes to rest after traveling 40.0 m. What is the net force on the car during its acceleration opposite to the motion? 1000 kg

v2=v20+2ax⇒a=−7.80m/s2Fnet=−7.80×103N

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10 i N in the x direction
-2 i N in the x direction
-4 j N in the y direction
Find the acceleration of the body of mass 5.0 kg shown below.

a=1.6i-.8j

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A rocket sled accelerates at a rate of 49.0m/s2
. Its passenger has a mass of 75.0 kg. (a) Calculate the horizontal component of the force the seat exerts against his body. Compare this with his weight using a ratio. (b) Calculate the direction and magnitude of the total force the seat exerts against his body.

3675 735
5.00times greater than weight
;
b. Fnetθ==3750N11.3°from horizontal

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A body of mass 2.00 kg is pushed straight upward by a 25.0 N vertical force. What is its acceleration?

2.7

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A body with a mass of 10.0 kg is assumed to be in Earth’s gravitational field with g=9.80m/s2 . What is the net force on the body if there are no other external forces acting on the object?

A baseball catcher is performing a stunt for a television commercial. He will catch a baseball (mass 145 g) dropped from a height of 60.0 m above his glove. His glove stops the ball in 0.0100 s. What is the force exerted by his glove on the ball?

497

(a) What net external force is exerted on a 1100.0-kg artillery shell fired from a battleship if the shell is accelerated at 2.40×104m/s2? (b) What is the magnitude of the force exerted on the ship by the artillery shell, and why?

2.64times 10^7

A bird has a mass of 26 g and perches in the middle of a stretched telephone line. using the equation T=mg/2sinθ . Determine the tension when (b) θ=5° and (c) θ=0.5° . Assume that each half of the line is straight.

5-->1.5 0.5-->14.5 or 15

Consider the baby being weighed in the following figure. (a) What is the mass of the infant and basket if a scale reading of 55 N is observed? (b) What is tension T1 in the cord attaching the baby to the scale? (c) What is tension T2 in the cord attaching the scale to the ceiling, if the scale has a mass of 0.500 kg?

m=5.61 t1=55 t2=59.91

What force must be applied to a 100.0-kg crate on a frictionless plane inclined at 30° to cause an acceleration of 2.0m/s2 up the plane?

690

Two blocks are at rest and in contact on a frictionless surface. Block 𝐴 A has a mass of 3 kg, and block 𝐵 B has a mass of 5 kg. A horizontal force of 30 N is applied to block 𝐴 Find the acceleration of the system. What is the force that block B experiences?

The acceleration of the system is 3.75 The force that block B experiences is 18.75

Two blocks are in contact on a frictionless surface. Block X has a mass of 4 kg, and block Y has a mass of 6 kg. A horizontal force of 40 N is applied to block X. Find the acceleration of the system. What is the force that block 𝑌 Y experiences?

The acceleration of the system is 4 . The force that block Y experiences is 24

as shown below two idnetical sorung each with a spring constant of 20 n/m supports a 15 N wight (a.)whats is the tension in spring A (b.)what is the amount of strech from the rest poistion

7.5 N and 0.375

a rope is used to lift a 50 kg box with an upward acceleartion of 2.3 m/s^2 (a.) what is the tension in the rope ? (b.) what would the tension be in the rope if the box descended slwoy with a downward acceleaqrtion of 0.75 m/s^2

a-->605 b-->452.5

A 1.5 kg model helicopter has a velocity of 5j m/s at = 0 It is accelerated at a constant rate for 2s after which it has a velocity of (6i + 13j ) m/s. What is the magnitude of the resultant force acting on the helicopter during this time interval? (A) F = (3i + 4j ) N (B) F = (7.5j ) N (C) F = (4i − 4j ) N (D) F = (4.5i + 6j ) N (E) F = (5i + 8j ) N

(B) F = (7.5j ) N

The Atwood machine consists of a rope running over a pulley, with two objects of different mass attached. Consider the pulley to be frictionless and m1 = 2 Kg and m2 = 4 Kg. (a) If is released, what will its acceleration be? (b) What is the tension in the string? (A) a = 9.8 m/s2; T = 39.2 N (B) a = 4.9 m/s2; T = 29.4 N (C) a = 3.3 m/s2; T = 26.1 N (D) a = 2.5 m/s2; T = 23.2 N (E) a = 0 m/s2; T = 19.8 N

The Atwood machine consists of a rope running over a frictionless pulley, with two objects of different mass attached. Consider the pulley to be frictionless, and the masses are: m1=5kg m2=7kg (a) If released, what will the acceleration be? (b) What is the tension in the string?

(a)1.6 m/s^2 (b.)57N

A 30.0-kg girl in a swing is pushed to one side and held at rest by a horizontal force F⃗ so that the swing ropes are 30.0° with respect to the vertical. (a) Calculate the tension in each of the two ropes supporting the swing under these conditions. (b) Calculate the magnitude of F⃗ .

A-->169 or 170 B-->169 or 170

Three forces act on an object, considered to be a particle, which moves with constant velocity v=(3iˆ−2jˆ)m/s. Two of the forces are F⃗ 1=(3iˆ+5jˆ)N and F⃗ 2=(4iˆ−7jˆ)N. Find the third force.

F3=-7i+2j

A 35.0-kg dolphin accelerates opposite to the motion from 12.0 to 7.50 m/s in 2.30 s to join another dolphin in play. What average force was exerted to slow the first dolphin if it was moving horizontally? (The gravitational force is balanced by the buoyant force of the water.)

-68.5 N

A large rocket has a mass of 2.00×106kg at takeoff, and its engines produce a thrust of 3.50×107N. (a) Find its initial acceleration if it takes off vertically. (b) How long does it take to reach a velocity of 120 km/h straight up, assuming constant mass and thrust?

a-->7.7 m/s^2 b-->4.33

A 2.50-kg fireworks shell is fired straight up from a mortar and reaches a height of 110.0 m. (a) Neglecting air resistance (a poor assumption, but we will make it for this example), calculate the shell’s velocity when it leaves the mortar. (b) The mortar itself is a tube 0.450 m long. Calculate the average acceleration of the shell in the tube as it goes from zero to the velocity found in (a). (c) What is the average force on the shell in the mortar?

a. 46.4 m/s b. 2.40×103m/s2 c. 5.99 × 103 N

An elevator filled with passengers has a mass of 1.70×103kg . (a) The elevator accelerates upward from rest at a rate of 1.20m/s2 for 1.50 s. Calculate the tension in the cable supporting the elevator. (b) The elevator continues upward at constant velocity for 8.50 s. What is the tension in the cable during this time? (c) The elevator accelerates opposite to the motion at a rate of 0.600m/s2 for 3.00 s. What is the tension in the cable during acceleration opposite to the motion?

a. 1.87×104N; b. 1.67×104N; c. 1.56×104N;

A student’s backpack, full of textbooks, is hung from a spring scale attached to the ceiling of an elevator. When the elevator is accelerating downward at 3.8m/s2 , the scale reads 60 N. (a) What is the mass of the backpack? (b) What does the scale read if the elevator moves upward while speeding up at a rate 3.8m/s2 ? (c) What does the scale read if the elevator moves upward at constant velocity? (d) If the elevator had no brakes and the cable supporting it were to break loose so that the elevator could fall freely, what would the spring scale read?

a. 10 kg; b. 136 N; c. 98 N; d. 0

A roller coaster car starts from rest at the top of a track 30.0 m long and inclined at 20.0° to the horizontal. Assume that friction can be ignored. (a) What is the acceleration of the car? (b) How much time elapses before it reaches the bottom of the track?

a. 3.35m/s2 ; b. 4.2 s

Two blocks are connected by a massless rope as shown below. The mass of the block on the table is 4.0 kg and the hanging mass is 1.0 kg. The table and the pulley are frictionless. (a) Find the acceleration of the system. (b) Find the tension in the rope. (c) Find the speed with which the hanging mass hits the floor if it starts from rest and is initially located 1.0 m from the floor.

a. 2.0m/s2; b. 7.8 N; c. 2.0 m/s

A 2.00 kg block (mass 1) and a 4.00 kg block (mass 2) are connected by a light string as shown; the inclination of the ramp is 40.0° . Friction is negligible. What is (a) the acceleration of each block and (b) the tension in the string?

a. 4.43m/s2 (mass 1 accelerates up the ramp as mass 2 falls with the same acceleration); b. 21.5 N

A 3.00 kg block (mass 1) is placed on a frictionless incline of 30.0 ∘ 30.0 ∘ , and a 5.00 kg block (mass 2) hangs vertically. The two blocks are connected by a light string. Assume the string is massless and inextensible. What is: (a) The acceleration of each block. (b) The tension in the string.

(a) The acceleration of each block is 4.29m/s2 . (b) The tension in the string is 27.6N

An elevator filled with cargo has a mass of 2.00×10^3kg (a) The elevator accelerates upward from rest at a rate of 1.50 m/s^2 for 2.00s Calculate the tension in the cable supporting the elevator during this acceleration. (b) The elevator then moves upward at a constant velocity for 6.00s.What is the tension in the cable during this time? (c) Finally, the elevator accelerates downward at a rate of 0.800m/s2 for 4.00s What is the tension in the cable during this downward acceleration?

(a) Tension during upward acceleration = 2.262 × 10⁴ N (b) Tension during constant velocity = 1.962 × 10⁴ N (c) Tension during downward acceleration = 1.802 × 10⁴ N

A sled starts from rest at the top of a hill that is 40.0 m long and inclined at 15.0° to the horizontal. Assume that friction can be ignored. (a) What is the acceleration of the sled? (b) How much time elapses before it reaches the bottom of the hill?

(a) Acceleration of the sled = 2.54m/s2 (b) Time to reach the bottom = 5.61s

A 3.0 kg block is on a perfectly smooth ramp that makes an angle of 25 ∘ 25 ∘ with the horizontal. (a) What is the block's acceleration down the ramp and the force of the ramp on the block? (b) What force applied upward along and parallel to the ramp would allow the block to move with constant velocity?

(a) Acceleration down the ramp = 4.14m/s2 , Normal force = 26.64N (b) Force required for constant velocity = 12.39N

The two blocks are attached to each other by a massless string that is wrapped around a frictionless pulley. When the bottom 4 kg block is pulled to the left by the constant force the top 2 kg block slides across it to the right. Find the magnitude of the force necessary to move the blocks at constant speed. Assume that the coefficient of kinetic friction between all surfaces is 0.4.

23.52 N.

Calculate the centripetal force exerted on a 900 kg car that negotiates a 500 m radius curve at v = 25 m/s. (b) Assuming an unbanked curve, find the minimum static coefficient of friction between the tires and the road, static friction being the reason that keeps the car from slipping Formula Fc=mv^2 /r

(a)1125 (b)0.127

a. 10.0 N; b. 97.0 N

. Consider the 65.0-kg ice skater being pushed by two others shown below. (a) Find the direction and magnitude of Ftot, the total force exerted on her by the others, given that the magnitudes F1 and F2 are 26.4 N and 18.6 N, respectively. (b) What is her initial acceleration if she is initially stationary and wearing steel-bladed skates that point in the direction of Ftot? (c) What is her acceleration assuming she is already moving in the direction of Ftot? (Remember that friction always acts in the direction opposite that of motion or attempted motion between surfaces in contact.)

a. 32.3 N, 35.2°; b. 0;.496 c. 0.301m/s2 in the direction of F⃗ tot

A machine at a post office sends packages out a chute and down a ramp to be loaded into delivery vehicles. (a) Calculate the acceleration of a box heading down a 10.0° slope, assuming the coefficient of friction for a parcel on waxed wood is 0.100. (b) Find the angle of the slope down which this box could move at a constant velocity. You can neglect air resistance in both parts.

a. 0.737m/s2; b. 5.71°

(a) A 22.0-kg child is riding a playground merry-go-round that is rotating at 40.0 rev/min. What centripetal force is exerted if he is 1.25 m from its center? (b) What centripetal force is exerted if the merry-go-round rotates at 3.00 rev/min and he is 8.00 m from its center? (c) Compare each force with his weight.

a. 483 N; b. 17.4 N; c. 2.24, 0.0807

What is the ideal banking angle for a gentle turn of 1.20-km radius on a highway with a 105 km/h speed limit (about 65 mi/h), assuming everyone travels at the limit?

4.14°

(a) What is the radius of a bobsled turn banked at 75.0° and taken at 30.0 m/s, assuming it is ideally banked? (b) Calculate the centripetal acceleration. (c) Does this acceleration seem large to you?

. a. 24.6 m; b. 36.6m/s2; c. 3.73 times g

If a car takes a banked curve at less than the ideal speed, friction is needed to keep it from sliding toward the inside of the curve (a problem on icy mountain roads). (a) Calculate the ideal speed to take a 100.0 m radius curve banked at 15.0° . (b) What is the minimum coefficient of friction needed for a frightened driver to take the same curve at 20.0 km/h?

a. 16.2 m/s; b. 0.234

Railroad tracks follow a circular curve of radius 500.0 m and are banked at an angle of 5.0° . For trains of what speed are these tracks designed?

20.7 m/s

A car rounds an unbanked curve of radius 65 m. If the coefficient of static friction between the road and car is 0.70, what is the maximum speed at which the car can traverse the curve without slipping?

21 m/s

The terminal velocity of a person falling in air depends upon the weight and the area of the person facing the fluid. Find the terminal velocity (in meters per second and kilometers per hour) of an 80.0-kg skydiver falling in a headfirst position with a surface area of 0.140m2 .

. 115 m/s or 414 km/h

A 560-g squirrel with a surface area of 930cm2 falls from a 5.0-m tree to the ground. Estimate its terminal velocity. (Use a drag coefficient for a skydiver falling feet first.) What will be the velocity of a 56-kg person hitting the ground, assuming no drag contribution in such a short distance?

v=9.9

We consider a car driving on a highway with a speed of 72 Km per hour. Now, if you put your hand outside of the window, what is the air drag force on your hand? We assume air density ρ = 1.21 Kg/m3 and its drag coefficient is has an area of 400 cm2. = 0.7. Your hand (A) 1.2 N (B) 3.5 N (C) 6.8 N (D) 9.8 N (E) 12. N

Assume the density of air is ρ = 1.21 Kg/m3. A 75 kg skydiver descending head first has a cross- 2 sectional area of approximately A = 0.18 m2 and a drag coefficient of approximately is his terminal velocity?

98.5 m/s.

Two blocks, one with mass m_1 = 5 \, \text{kg} and the other with mass m_2 = 3 \, \text{kg}, are connected by a massless string over a frictionless pulley. The bottom block is pulled to the right by a constant force F_{\text{applied}}, and the top block slides to the right across the bottom block. The coefficient of kinetic friction between the blocks and the surfaces is \mu_k = 0.3 . Find the magnitude of the applied force F_{\text{applied}} necessary to move the blocks at constant speed

32.34

Question: A 5.0 kg block is placed on a horizontal surface with a coefficient of friction of 0.40. A horizontal force is applied to the block. If the applied force is 30 N, calculate: The acceleration of the block. The force of friction acting on the block.

a-->2.08 m/s^2 b-->19.6

A 10.0 kg box is placed on a 25.0° incline. The coefficient of friction between the box and the surface is 0.30. A force of 100 N is applied parallel to the incline to move the box. Calculate: The acceleration of the box. The force of friction acting on the box.

a-->3.3 b-->26.64

A car is driving around a banked curve with an angle of 40.0° at a speed of 20.0 m/s. The radius of the turn is 100 meters. What is the ideal speed for the car to take the turn without relying on friction? Calculate the centripetal acceleration of the car. How does the centripetal acceleration compare to gravity?

The ideal speed for the car to take the turn is approximately 28.6 m/s. The centripetal acceleration of the car is 4.0 m/s². The centripetal acceleration is about 0.41 times the acceleration due to gravity

: A car is traveling at 80 km/h on a highway that curves with a radius of 500 meters. What is the ideal banking angle for the curve, assuming there is no friction and the car is traveling at the speed limit?

5.73

You lift an oversized library book, weighing 20 N, 1 m vertically down from a shelf, and carry it 3 m horizontally to a table. How much work does gravity do on the book? (b) When you’re finished, you move the book in a straight line back to its original place on the shelf. What was the total work done against gravity, moving the book away from its original position on the shelf and back again?

a.)20J b.)0

A 5 kg body has three times the kinetic energy of an 8 kg body. Calculate the ratio of the speeds of these bodies (A) 2.2 (B) 1.0 (C) 3.0 (D) 4.8 (E) 6.2

A-2.2

When released, a 1 kg block slides down the path shown below, reaching the bottom with a speed of 4 m/s. How much work does the force of friction do? The height is 2 (A)- 5.6 J (B)-11.6 J (C)- 9.8 J (D)- 8.0 J (E)-19.6 J

b.)-11.6 J

Example How much power must an automobile engine expend to move a 1200 kg car up a 30 degree grade at 72 km/h?

1176

A man of mass 80 kg runs up a flight of stairs h=20 m high in 10 s. How much is the averaged power used to lift the man? (A)80 W (B) 196 W (C) 1568 W (D) 1960 W (E) 3200 W

How much work does a supermarket checkout attendant do on a can of soup he pushes 0.600 m horizontally with a force of 5.00 N?

3 J

(a) Calculate the work done on a 1500-kg elevator car by its cable to lift it 40.0 m at constant speed, assuming friction averages 100 N. (b) What is the work done on the elevator car by the gravitational force in this process? (c) What is the total work done on the elevator car?

a. 592 kJ; b. –588 kJ; c. 0 J

Calculate the work done by an 85.0-kg man who pushes a crate 4.00 m up along a ramp that makes an angle of 20.0° with the horizontal (see below). He exerts a force of 500 N on the crate parallel to the ramp and moves at a constant speed. Be certain to include the work he does on the crate and on his body to get up the ramp.

3.14 kJ or 3144 J

A shopper pushes a grocery cart 20.0 m at constant speed on level ground, against a 35.0 N frictional force. He pushes in a direction 25.0° below the horizontal. (a) What is the work done on the cart by friction? (b) What is the work done on the cart by the gravitational force? (c) What is the work done on the cart by the shopper? (d) Find the force the shopper exerts, using energy considerations. (e) What is the total work done on the cart?

b. 0 J; c. 700 J; d. 38.6 N; e. 0

A constant 20-N force pushes a small ball in the direction of the force over a distance of 5.0 m. What is the work done by the force?

100J

A 5.0-kg box rests on a horizontal surface. The coefficient of kinetic friction between the box and surface is μK=0.50. A horizontal force pulls the box at constant velocity for 10 cm. Find the work done by (a) the applied horizontal force, (b) the frictional force, and (c) the net force.

a. 2.45 J; b. – 2.45 J; c. 0 J

How much work is done against the gravitational force on a 5.0-kg briefcase when it is carried from the ground floor to the roof of the Empire State Building, a vertical climb of 380 m?

18.6 kJ

(a) How fast must a 3000-kg elephant move to have the same kinetic energy as a 65.0-kg sprinter running at 10.0 m/s? (

a. 1.47 m/s;

Calculate the kinetic energies of (a) a 2000.0-kg automobile moving at 100.0 km/h; (b) an 80.-kg runner sprinting at 10. m/s; and (c) a 9.1×10−31-kg electron moving at 2.0×107m/s.

a. 772 kJ; b. 4.0 kJ; c. 1.8×10−16J

An 8.0-g bullet has a speed of 800 m/s. (a) What is its kinetic energy? (b) What is its kinetic energy if the speed is halved?

a. 2.6 kJ; b. 640 J

A car’s bumper is designed to withstand a 4.0-km/h (1.1-m/s) collision with an immovable object without damage to the body of the car. The bumper cushions the shock by absorbing the force over a distance. Calculate the magnitude of the average force on a bumper that collapses 0.200 m while bringing a 900-kg car to rest from an initial speed of 1.1 m/s.

2.72 kN

Using energy considerations, calculate the average force a 60.0-kg sprinter exerts backward on the track to accelerate from 2.00 to 8.00 m/s in a distance of 25.0 m, if he encounters a headwind that exerts an average force of 30.0 N against him.

102 N

A constant 10-N horizontal force is applied to a 20-kg cart at rest on a level floor. If friction is negligible, what is the speed of the cart when it has been pushed 8.0 m?

2.8 m/s

An 8.0-g bullet with a speed of 800 m/s is shot into a wooden block and penetrates 20 cm before stopping. What is the average force of the wood on the bullet? Assume the block does not move.

12.8 kN

A man of mass 80 kg runs up a flight of stairs 20 m high in 10 s. (a) how much power is used to lift the man?

a. 1.57 kW;

A girl pulls her 15-kg wagon along a flat sidewalk by applying a 10-N force at 37° to the horizontal. Assume that friction is negligible and that the wagon starts from rest. (a) How much work does the girl do on the wagon in the first 2.0 s. (b) How much instantaneous power does she exert at t=2.0s ?

a. 8.51 J; b. 8.51 W

Scenario: Imagine you have a spring with a known spring constant 𝑘 = 100 N/m k=100N/m. You apply a force to stretch the spring. Example: If you apply a force of 50 N, how much does the spring stretch?

x=0.5m

A shopper pushes a grocery cart 30.0 m at constant speed on level ground, against a 45.0 N frictional force. The shopper pushes in a direction 20.0° below the horizontal. (a) What is the work done on the cart by friction? (b) What is the work done on the cart by the gravitational force? (c) What is the work done on the cart by the shopper? (d) Find the force the shopper exerts, using energy considerations. (e) What is the total work done on the cart?

a)-1350J b)0J c)1350J d)47.9N e)0J

A 50 kg box is sliding down a 25° inclined plane. The coefficient of kinetic friction between the box and the incline is 0.3. (a) Determine the acceleration of the box as it slides down the incline. (b) If the box starts from rest, how fast will it be moving after 4 seconds?

Acceleration: 1.47 1.47 m/s² Velocity after 4 seconds: 5.89 5.89 m/s

a crate with mass m is sliding down a 30 degree inclinced plane the coefficent of kinetric friction betrween the crate and the incline is 0.4

1.50 m/s².

Exam Two Flashcards

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