Physics 201 MWF10:20 Fall 2001 (Ford)

Exam III Chapts. 5-7 in Cutnell and Johnson 5th ed.

Multiple choice questions. Circle the correct answer. No work need be shown and no partial credit will be given.

(3 pts) 1. An object travels at constant speed in a circular path. The acceleration of the object is

a) zero since the speed is constant
b) nonzero and directed radially outward away from the center of the path
c) nonzero and directed radially inward toward the center of the path <--------
d) nonzero and in the direction tangent to the path


(3 pts) 2. A small coin rests on a disk that is rotating at a constant rate about an axis through its center. When the coin is in the position shown the friction force on the coin is

a) zero
b) nonzero and to the left <---------
c) nonzero and to the right


3. A box slides down an incline that is inclined at 37° above the horizontal.

(2 pts) As the box slides down the incline, from point A to point B, the work done by the normal force on the box is

a) zero <----------
b) positive
c) negative


(2 pts) As the box slides down the incline, from point A to point B, the work done by the gravity force on the box is

a) zero
b) positive <---------
c) negative


(3 pts) 4. A wrecking ball swings at the end of a 10 m long cable. As the ball moves from point A to point B, the work done on the ball by the tension in the rope is

a) zero <--------
b) positive
c) negative


(4 pts) 5. Two satellites, A and B, orbit the earth in circular orbits. The speed of satellite A is 5 × 10³ m/s and the speed of satellite B is 8 × 10³ m/s. Which satellite is farther from the surface of the earth?

a) A <-----------
b) B
c) they are the same height


(3 pts) 6. A man is standing at one edge of a floating raft that is stationary. Neglect any horizontal force that the water exerts on the raft, so the man and the raft form an isolated system. As the man walks due east to the other side of the raft, the center of mass of the man plus raft system

a) doesn't move <--------
b) moves east
c) moves west


On the following problems show all your work. Partial credit will be given if earned. Write your answers in the blanks provided.

(16 pts) 7. A pitcher throws a 0.2 kg baseball and just before it is hit by the batter the ball has a horizontal velocity of 20 m/s and is 1.0 m above the ground. The bat hits the ball. After being hit, when the ball is 16.0 m above the ground its speed is 30 m/s. How much work did the bat do on the ball?

Ans. ____79.4 J____


(20 pts) 8. A swing ride at a carnival consists of chairs that are swung in a horizontal circle by 10 m long cables attached to a vertical rotating pole, as shown in the sketch. The cable attached to a chair makes an angle of 53° relative to the vertical pole and the tension in this cable is 300 N.

a) What is the total mass of the chair and its occupant?

Ans. ____18.4 kg_____

b) What is the acceleration of the chair?

Ans.___13.0 m/s²___

c) How much time does it take the chair to complete one revolution?

Ans. ___4.93 s___


(22 pts) 9. A small block with mass 0.2 kg is released from rest at point A that is at the top of a curved track that has the shape of a semicircle of radius 4.0 m. When the block reaches point B at the lowest point of the track its speed is 8.0 m/s.

a) During the motion of the block from point A to point B, how much work is done on the block by the friction force?

Ans. ___-1.44 J____

b) What is the magnitude of the normal force that the track exerts on the block when the block is moving through point B?

Ans.____5.16 N___


(22 pts) 10. A mine car whose mass is 500 kg is rolling at a constant speed of 2.0 m/s to the left on a horizontal track. The friction force exerted by the track on the car can be neglected. A 300 kg chunk of coal has a velocity of 8.0m/s at 37° below the horizontal when it leaves the chute 4.0 m above the bottom of the car, as shown. The chunk of coal lands in the car.

a) What is the speed of the chunk of coal just before it strikes the bottom of the car. Neglect air resistance.

Ans. ____11.9 m/s___

b) What is the velocity (magnitude and direction) of the car after the chunk of coal has come to rest relative to the car?

Ans. magnitude ___1.15 m/s___

direction (left or right?) __to the right___