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Physics 111 > Exam 3 > Flashcards

Exam 3 Flashcards

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1
Q

You are holding a 1 kg rock and standing at the top of a cliff. You drop the rock off the cliff and it falls a distance 10 m. In this problem you can ignore air resistance. What is the change in the kinetic energy of the rock as it falls that distance?

A

about 100 J

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2
Q

Two objects are dropped from rest from height h. If object A is twice the mass of object B what can be said about their kinetic energies as they hit the ground

A

about A has twice the kinetic energy of object B

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3
Q

You have a spring with a spring constant 6480 N/m. If you want to store 225 J of energy in this spring, should you compress it or stretch it?

A

Either can be done

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4
Q

Two masses sit at the top of two frictionless inclined planes that have different angles, as shown in the figure. What can be said about the speeds of two masses at the bottom of their respective paths?

A

The two balls are traveling the same speed

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5
Q

Two masses sit at the top of two frictionless inclined planes that have different angles, as shown in the figure. Which mass gets to the bottom first?

A

Mass two

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6
Q

You stand on the edge of a very tall building with three rocks, which you are going to throw off the edge. You throw the first rock straight outwards, the second rock at an angle 60° above the horizontal, and the third rock 30° below the horizontal. If you throw all three rocks with the same initial speed, which will be moving the fastest when it hits the ground?

A

They will all have the same speed

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7
Q

A ball drops some distance and gains 30 J of kinetic energy. DO NOT ignore air resistance. How much gravitational potential energy did the ball lose?

A

more than 30 J

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8
Q

The conservation of momentum is most closely related to

A

Newton’s 3rd Law

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9
Q

Your pet hamster sits on a record player that has constant angular speed. If the hamster moves to a point twice as far from the center, then its linear speed……

A

doubles

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10
Q

The center of mass of a human body is located at a point

A

that changes as a person bends over

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11
Q

the starting point and ending points are the same?

A

the total work is zero

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12
Q

What is true about the work done by a conservative force?

A

It can always be expressed as the difference between the initial and final values of a potential energy function

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13
Q

What is true about the work done by a conservative force regarding the path of the body?

A

It is independent of the path of the body and depends only on the starting and ending points

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14
Q

It is correct to say that impulse is equal to

A

the change in momentum it produces

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15
Q

As you are leaving a building, the door opens outward. If the hinges on the door are on your right, what is the direction of the angular velocity of the door as you open it?

A

down

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16
Q

To catch a ball, a baseball player extends the hand forward before impact with the ball and then lets it ride backward in the direction of the ball’s motion. Doing this reduces the force of impact on the players hand principally because the

A

time of impact is increased

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17
Q

A baseball is thrown vertically upward and feels no air resistance. As it is rising,…..

A

its momentum and its mechanical energy are conserved

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18
Q

A spring with a constant of 200N/m is compressed 8 cm. How much energy does it store?

A

1/2Kd^2

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19
Q

The force on an apple hitting the ground depends upon

A
  • whether or not the apple bounces
  • the speed of the apple just before it hits
  • the time of impact with the ground
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20
Q

Which will roll down an incline in the shortest time, a can filled with water or the same can filled with ice?

A

water

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21
Q

Is it possible for a system to have negative potential energy?

A

Yes, since the choice of the zero potential energy is arbitrary

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22
Q

When a rigid body rotates about a fixed axis, all the points in the body have the same….

A

angular acceleration

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23
Q

What is the general equation for conservation of energy?

A

K1+U1+W other = K2+U2

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24
Q

Nonconservative forces CANNOT______

A

be represented in terms of potential energy

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25
Conservative forces are ____ while nonconservative forces are ______
reversible | nonreversible
26
______ depends of path taken
friction
27
What is the definition of momentum?
p=mv
28
The net force (vector sum of all forces) acting on a particle equals
the time rate of change of momentum of the particle
29
Momentum is a
vector
30
Momentum is proportional to
velocity
31
The impulse is
the product of the net force and the time interval
32
Impulse is a _____ and has the units _____
vector | N s
33
What is the impulse momentum theorem?
J = p2-p1
34
Force times ______ changes kinetic energy
distance
35
Force times ____ changes momentum
time
36
Forces that act within the | system are
internal forces
37
Forces that act on the | system from outside are
external forces
38
______ cannot change the total momentum
Internal forces
39
An ______ has no external forces
isolated system
40
If the vector sum of the external forces on a system is ____, the total momentum of the system is ______
zero | constant
41
What are the two types of collisions in an isolated system?
- elastic collisions | - inelastic collisions
42
How can you identify a collision in an isolated system?
- Look for “frictionless” or “brief” as descriptions | - Momentum is conserved
43
What are the characteristics of an elastic collision?
- Forces between objects are conservative | - Momentum and kinetic energy are conserved
44
What are the characteristics of an inelastic collision?
- Some energy lost - Momentum is conserved - Objects that stick together undergo “completely inelastic collisions.”
45
What are two examples of elastic collisions?
- Billiard balls | - Newton’s cradle demonstration
46
What is the equation for elastic collisions?
(VB2x - VA2x) = -(VB1x - VA1x)
47
The center of mass is defined ______
mathematically
48
The total momentum P is equal to the
total mass times the velocity of the center of mass
49
Define a rigid body
the rotating object has a perfectly definite and unchanging shape and size. This means no twisting, stretching, bending, or compressing, etc
50
One complete cycle of 360° is
one revolution
51
One complete revolution is
2π radians
52
360° equals
2πradians
53
What does theta equal
s/r
54
How do we denote angular displacement? What are the units?
theta | radians
55
How do we donate angular velocity? What are the units?
ω (omega) radians/s rpm
56
Angular velocity is a _____
vector
57
How do we denote angular acceleration? What are the units?
α | radians per second^2
58
Angular acceleration is a ______
vector
59
The angular acceleration vector will be _____ or ______ to the angular velocity vector
parallel | Antiparallel
60
If angular acceleration and velocity are in the same direction......
the rotation is speeding up
61
If angular acceleration and velocity are in the opposite direction......
the rotation is slowing down
62
What is the equation for linear speed?
V = rω
63
What is the equation for linear acceleration?
Atan = rα
64
What is the equation for centripetal acceleration?
Arad = ω^2r
65
What is the equation for rotational kinetic energy?
1/2Iω^2
66
The known variables are the bullet's mass m, the Pendulum's mass M, and the height to which the block and bullet swing, determined by the length of the pendulum L and final angle θ. What two principles are are necessary to solve for the bullets velocity?
Conservation of Momentum and Conservation of Energy
67
Two ladybugs are crawling across a record that is on a record player. The record player is turned on and it reaches a constant angular velocity. If the male ladybug is all the way at the edge and the female ladybug is halfway between the center and the edge. Which has a greater magnitude of acceleration?
the male ladybug
68
Two ladybugs are crawling across a record that is on a record player. The record player is turned on and it reaches a constant angular velocity. If the male ladybug is all the way at the edge and the female ladybug is halfway between the center and the edge. If they both have the same mass, which one has to grip the record tighter to keep from falling off?
the male ladybug
69
Two ladybugs of the same mass are on a record that is on a record player. The record player is turned on and it reaches a constant velocity. If the male ladybug is all the way at the edge and the female ladybug is halfway between the center and the edge, what can be said about their moments of inertia?
The male ladybug's moment of inertia is four times that of the females
70
Consider two equal masses M attached to the ends of massless rods, of length R, as shown in the figure. Treat the two masses as point masses, each located at a distance R from the point where the rods touch. What is the moment of inertia of this system, about an axis perpendicular to the page and passing through the point where the rods touch?
2MR^2
71
A girl with a mass of 60kg throws a ball of mass .8kg against a wall. The ball strikes horizontally with a speed of 11 m/s and it bounces back with the same speed. The ball is in contact with the wall 0.05s. What is the average force exerted on the wall by the ball?
F = m(V1 - V2)/t
72
What is the angular speed?
W = Wo+αt
73
Through what angle does the flywheel turn?
theta = thetao+Wot+1/2αt^2 | 360/2pi rad
74
What is the angular speed of the flywheel after 10 rev?
W^2 = Wo^2+2α(theta -thetao) | 2pi rad/1 rev
75
What equation is used to find the distance of the horizontal region?
K1 + Ug1 + Wother = 0 1/2mVo^2 + mgh2 - Ffd = 0 1/2Vo^2 + gh2 = uKgd
76
How do you find the position of center of mass?
Xcm = m1x1 + m2x2 + m3x3/(m1 + m2 + m3) Ycm = m1y1 + m2y2 + m3y3/(m1 + m2 + m3)
77
How do you find the moment of inertia of the system when particles are moving around the organ with the same angular velocity?
``` r1 = sqrt(x1^2 + y1^2) r2 = sqrt(x2^2 + y2^2) r3 = sqrt(x3^2 + y3^2) ``` I = m1(r1)^2 + m2(r2)^2 + m3(r3)^2
78
How do you find the speed of a block at the bottom on an incline when there is a spring?
``` Ug1 = K2 y1 = Lsin(theta) Ff = uKFn (Fn = mg) mgLsin(theta) = 1/2mV2^2 V2 = sqrt(2gLsin(theta)) ```
79
How do you find how far a block compresses a spring before coming to rest?
``` Ug1 + Wother = Uel3 mgLsin(theta) - Ff(d+x) = 1/2Kx^2 *use quadratic formula* a = 1/2Kx^2 b = uKmgx c = uKmgd - mgLsin(theta) ```
80
How do you find the Va2y of hockey puck A? | How do you find the Va2x of hockey puck A?
Va2sin(thetaA) | Va2cos(thetaA)
81
How do you find Vb2x of hockey puck B after the collision?
MaVa1x + MbVb1x = MaVa2x + MbVbx | Vb2x = Ma(Va1x -Va2x)/Mb
82
How do you find Vb2y of hockey puck B after the collision?
MaVa1y + MbVb1y = MaVa2y + MbVby | Vb2y = -Ma(Va2y)/Mb
83
How do you find the total speed of puck B after the collision?
Vb = sqrt(Vb2x^2 + Vb2y^2)
84
How do you find the direction of puck B after the collision?
``` tan(theta) = Vb2y/Vb2x theta = tan-1(Vb2y/Vb2x) ```
85
How do you find the max height of a basketball thrown straight up?
``` E = mghmax 1/2mV^2 = mghmax max = 1/2V^2/g ```
86
How do you find the final velocity of a skier?
Ke1 + Pe1 + Wother = Ke2 + Pe2 1/2mVo^2 -Ffd = 1/2mVf^2 + mgh Vf = sqrt(Vo^2 -2gh (1 + uk (cos/sin))
87
How do you find the distance a spring is compressed on an inclined plane?
W = deltaK mgsin(theta)x + 1/2K(delta s)^2 = 1/2mV1^2 *solve for x* ds = (x - delta s)
88
How do you find the fiction coefficient of an inclined plane?
W = delta K delat K = 0 -1/2mV^2 W = Wg + Wk -mgsin(theta) -umgcos(theta)ds = delta K *solve for u*
89
What does the frictional force equal?
``` Ffk = ukFn (Fn = mgcos(theta)) ```
90
how is Ke = Espring written?
1/2mV2 = 1/2Kd^2
91
How is Pe = Ke written?
mgh = 1/2 mV^2
92
What does Kef equal?
Kei + Pe | 1/2mV^2 + mgh
93
what does total E equal?
Ke + Pe | 1/2mVo^2 + mgh
94
What is the equation for momentum?
P=mv
95
What can I equal?
m(sqrt(2gh2) + sqrt(2gh1)) | Ft
96
how is Pi = Pf written?
M1V1 = (M1 +M2)Vf
97
What is the angular acceleration of each hand on a clock?
zero
98
What does α equal?
(W2 -W1)/t

Physics 111 (4 decks)

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