physics ch 5

8. A 50.0-kg block is being pulled up a 13.0° slope by a force of 250 N which is parallel to the slope. The coefficient of kinetic friction between the block and the slope is 0.200. What is the acceleration of the block?

e. 0.886 m/s2

21. For an object that travels at a fixed speed along a circular path, the acceleration of the object is

e. larger in magnitude the smaller the radius of the circle.

18. A ball is tied to the end of a cable of negligible mass. The ball is spun in a circle with a radius 2.00 m making 0.700 revolutions per second. What is the centripetal acceleration of the ball?

a. 38.7 m/s2

4. A girl is whirling a ball on a string around her head in a horizontal plane. She wants to let go at precisely the right time so that the ball will hit a target on the other side of the yard. When should she let go of the string?

a. At the moment that the tangential velocity vector is directed exactly at the target

24. Consider a particle moving with constant speed such that its acceleration of constant magnitude is always perpendicular to its velocity.

a. It is moving in a circle.

2. When attempting to stop a car quickly on dry pavement, which of the following methods will stop the car in the least time?

a. Press the brakes as hard as possible without locking the wheels and rolling to a stop.

10. The coefficient of static friction is always larger than the coefficient of kinetic friction.

a. True

11. The force of static friction between two surfaces is parallel to the surface of contact, and in the direction that opposes relative motion.

a. True

12. It is often easier to keep a heavy object sliding than it is to start it sliding in the first place.

a. True

13. In problems involving a slope or inclined plane, the normal force is always perpendicular to the slope or the plane.

a. True

20. For uniform circular motion, the velocity and acceleration vectors are perpendicular to each other at every point in the path.

a. True

9. The force of friction between two surfaces is independent of the area of contact between the surfaces.

a. True

23. When an object experiences uniform circular motion, the direction of the acceleration is

a. is directed toward the center of the circular path.

6. A child pulls a 3.00-kg sled across level ground at constant velocity with a light rope that makes an angle 34.0° above horizontal. The tension in the rope is 5.00 N. Assuming the acceleration of gravity is 9.81 m/s2, what is the coefficient of friction between the sled and the ground?

b. 0.156

7. A box is sliding down an incline tilted at an angle 14.0° above horizontal. The box is sliding down the incline at a speed of 1.70 m/s. The coefficient of kinetic friction between the box and the incline is 0.380. How far does the box slide down the incline before coming to rest?

b. 1.16 m

19. A body moving with constant speed cannot be accelerating.

b. False

3. Sometimes it is said that water is removed from clothes in a spin dryer by centrifugal force throwing the water outward. Is this correct?

b. No

1. A heavy crate rests on the bed of a flatbed truck. When the truck accelerates, the crate remains where it is on the truck, so it, too, accelerates. What force causes the crate to accelerate?

b. Static friction between the crate and the truck bed

16. A packing crate slides down an inclined ramp at constant velocity. Thus we can deduce that

b. a frictional force is acting on it.

14. In problems involving a slope or inclined plane, the force due to gravity is always perpendicular to the slope or the plane.

b. false

5. A 60.0-kg mass person wishes to push a 100-kg mass box across a level floor. The coefficient of static friction between the person's shoes and the floor is 0.700. What is the maximum coefficient of static friction between the box and the floor such that the person can push horizontally on the box and cause it to start moving?

c. 0.420

25. A 2-kg ball is moving with a constant speed of 5 m/s in a horizontal circle whose radius is 50 cm. What is the magnitude of the net force on the ball?

c. 100 N

17. A 2-kg ball is moving with a constant speed of 5 m/s in a horizontal circle whose radius is 50 cm. What is the acceleration of the ball?

c. 50 m/s2

22. What type of acceleration does an object moving with constant speed in a circular path experience?

c. Centripetal acceleration

15. It is more difficult to start moving a heavy carton from rest than it is to keep pushing it with constant velocity, because:

c. μk < μs.