Final Exam

Question 1

A ball’s initial position is < 10, 4, -6 > m, and the ball’s velocity is < 3, -2, 4 > m/s.
What is the position of the ball 3 seconds later?
Assume that the ball’s velocity does not change significantly in this short time interval.

Answer 1

< 19, -2, 6 > m

Question 2

The figure below shows a motion diagram for an object. The number near each dot indicates the
clock reading in seconds when the object passes that location. The positive direction is defined
as to the right of the page. Which of the following is true about the object?

Answer 2

The object has negative acceleration before t = 3 and
positive acceleration after t = 3 s.

Question 3

The figure shows a graph of the velocity of an object as a function of time. What is the
displacement of the object from 0 s to 8.0 s?

Answer 3

60 m

Question 4

When a ball is thrown straight up with no air resistance, the acceleration at its highest point…

Answer 4

is downward.

Question 5

A projectile is fired from the origin with a velocity of 30.0 m/s at an angle of 45.0 degrees above
the horizontal.
What is the range of the projectile?

Answer 5

92 m

Question 6

A projectile is fired from the origin with a velocity of 20.0 m/s at an angle of 30.0 degrees above
the horizontal.
The projectile lands on a roof that is 4.00 m high.
What is the magnitude of the velocity when the projectile hits the roof?

Answer 6

17.9 m/s

Question 7

We pull a table cloth on a flat but rough table surface at a constant 1 m/s velocity. There is a
plate on the cloth that moves together with it at the same velocity. Which statement is
the
most accurate?

Answer 7

There is a kinetic friction force between the cloth and the
table, but there is no friction force between the plate and
the cloth

Question 8

If you pound a feather with a hammer, which one feels a greater force?

Answer 8

The size of the force is always exactly the same on both of
them.

Question 9

If a net force accelerates a 4.5 kg tool at 40 m/s , what acceleration would that same net force
give to an 18 kg tool?

Answer 9

10 m/s

Question 10

A golf club exerts an average horizontal force of 1000 N on a 0.045 kg golf ball that is initially at
rest on the tee. The club is in contact with the ball for 1.8 x 10 s.

Answer 10

40 m/s

Question 11

A 20 kg block on a frictionless incline is connected to a 15 kg mass by an ideal string that passes
over an ideal pulley, as shown in the diagram below. The block and mass are both motionless
and remain at rest. Which of the following is the correct pair of force diagrams for the mass and the block?

Answer 11

Block: 3 arrows in Y shape
Mass: 2 arrows up and down

Question 12

What is the tension in the string?

Answer 12

147 N

Question 13

An 82 kg warehouse crate is initially at rest when a fork truck begins to push it across the floor.
After 6 s, the crate slides at 3 m/s.
What force of friction acts on the crate if the fork truck applies 55N of force horizontally
to the crate?

Answer 13

14 N

Question 14

A block of mass m remains at rest on a rough inclined ramp that makes an angle θ with the
horizontal.
What must be true about the force of static friction f on the block?

Answer 14

f = mg sin θ

Question 15

Two masses are connected by a string which passes over a pulley with negligible mass and
friction.
One mass hangs vertically and one mass slides on a 30.0 degree frictionless incline.
The vertically hanging mass is 6.00 kg and the mass on the incline is 4.00 kg.

Answer 15

7.84 m/s2

Question 16

To good approximation, Earth orbits the Sun along a circular path at constant speed.
Which of the following is true then?

Answer 16

Earth’s velocity and acceleration are nonzero and orthogonal
to each other.

Question 17

A 1000 kg car is moving at 30 m/s around a horizontal unbanked curve whose diameter is 0.20
km. What is the magnitude of the friction force required to keep the car from sliding?

Answer 17

9000 N

Question 18

A 2000 kg car is traveling on a banked curved icy road without sliding.
The velocity of the car is 32.0 m/s and the road is banked at an angle of 20.0 degrees. The radius of curvature of the road is:

Answer 18

287 m

Question 19

A car moving at a steady 10 m/s on a level highway encounters a depression that has a circular
cross-section with a radius of 30 m. The car maintains its speed as it drives through the
depression.
What is the normal force exerted by the seat of the car on a 60 kg passenger when the car is at
the bottom of the depression?

Answer 19

790 N

Question 20

In a popular carnival ride called
The Centrifuge, shown below, riders stand against the inside wall
of a large cylinder, which starts spinning. The radius of the circle traveled by the riders is 5.0 m.
The coefficient of static friction between a person’s shirt and the wall of the ride is 0.8. At what speed must the riders be moving to not slip downward when the floor lowers?

Answer 20

7.8 m/s

Question 21

The graph in the figure shows the x component F of the net force that acts for 10 s on a 100
kg crate. What is the change in the momentum of the crate during the 10 s that this force acts?

Answer 21

-75 kg · m/s

Question 22

A rubber ball and a lump of clay have equal mass. They are thrown with equal speed against a
wall. The ball bounces back with nearly the same speed with which it hits. The clay sticks to the
wall. Which one of these objects undergoes the greater momentum change?

Answer 22

The ball

Question 23

Three objects are moving along a straight line as shown in the figure. Taking the positive
direction to be to the right, what is the total momentum of this system?

Answer 23

-14.0 kg · m/s

Question 24

A 100 g ball falls from a window that is 12 m above ground level and experiences no significant
air resistance as it falls. What is its momentum when it strikes the ground?

Answer 24

1.5 kg · m/s pointing downwards

Question 25

Matthew pulls his little sister Sarah along the horizontal ground in a wagon. He exerts a force on the wagon of 60.0 N at an angle of 37.0° above the horizontal. If he pulls her a distance of 12.0 m, how much work does Matthew do?

Answer 25

575 J

Question 26

Two men, Joel and Jerry, push against a car that has stalled, trying unsuccessfully to get it moving. Jerry stops after 10 min, while Joel is able to push for 5.0 min longer. Compare the work they do on the car.

Answer 26

Neither of them does any work.

Question 27

A 0.5 m solar panel produces approximately 50 W power on a sunny day. How long does it take for the panel to produce the amount of energy required to lift a 50 kg person up 1.0 m (assuming no energy losses)? Choose the time that is the closest to your calculation.

Answer 27

10 sec

Question 28

A 1500 kg car moving at 25 m/s hits an initially uncompressed horizontal ideal spring with spring constant (force constant) of 2.0 × 10 N/m. What is the maximum distance the spring compresses?

Answer 28

0.68 m

Question 29

In any collision (conserved means fixed and does not change):

Answer 29

Total momentum is conserved.

Question 30

Which of the following describes an inelastic collision? (conserved means fixed and does not change)

Answer 30

Total momentum is conserved, and total kinetic energy is not conserved.

Question 31

In the figure, determine the character of the collision. The masses of the blocks, and the velocities before and after, are shown. The collision is...

Answer 31

perfectly elastic.

Question 32

Two carts are involved in an inelastic collision. Cart A with a mass 1.0 kg hits cart B with a mass 0.5 kg. The two carts stick together after the collision and continue to move along together. Cart A has an initial velocity of 2.0 m/s and cart B is initially at rest. What is the final velocity of the two-cart system?

Answer 32

1.3 m/s

Question 33

A wheel is rotating at a constant rotational acceleration. Which of the following must be true?

Answer 33

The net torque exerted on the wheel is constant.

Question 34

A bar is pinned so that it can turn about its center with a rotational inertia of 1.6 kg*m . The bar is initially motionless, but it begins to spin when a constant 8 N*m torque is applied. Through what angle does the bar turn if the torque is applied for 2s?

Answer 34

10 rad

Question 35

A man in a gym is holding an 8.0 kg weight at arm’s length, a distance of 0.55 m from his shoulder joint. What is the torque about his shoulder joint due to the weight if his arm is held at 30° below the horizontal?

Answer 35

37 Nm

Question 36

A disk is in the x-y plane and rotates clockwise around the z axis. What direction is the angular momentum of the disk?

Answer 36

negative z direction

Question 37

A uniform, solid, cylindrical flywheel of radius 1.4 m and mass 15 kg rotates at 2.7 rad/s. What is the magnitude of the flywheel's angular momentum?

Answer 37

40 kg ∙ m /s

Question 38

A student sits on a barstool holding a bike wheel. The wheel is initially spinning CW in the horizontal plane (as viewed from above) with L = 25 kg /s. She now turns the bike wheel over 180 degrees. What happens?

Answer 38

she starts to spin CW

Question 39

Which force (A-E) has the largest magnitude torque applied to the wrench, measured about an axis centered on the bolt?

Answer 39

Force D

Question 40

A typical ten-pound car wheel has a moment of inertia of about 0.35 kg ∗ m . The wheel rotates about the axle at a constant angular speed making 50.0 full revolutions in a time interval of 4.00 s. What is the rotational kinetic energy of the rotating wheel?

Answer 40

1100 J