A 1. book is sitting on the very slick (frictionless) passenger seat of a car. The car is moving at a constant velocity. The driver suddenly hits his breaks. The book suddenly slides off the seat. Why? (a) A force acted on the book in the forward direction. (b) A force acted on the book in the backward direction. (c) A force acted on the car and the book in the forward direction. (d) A force acted on the car and the book in the backward direction. (e) No force acted on the book, so it continued to move at the same original velocity while the car slowed down. 2. A ball moves with a constant speed of 4 m/s around a circle of radius 0.25 m. What is the period of the rotation? (a) 0.1 s (b) 0.4 s (c) 0.7 s (d) 8 s (e) 2 s 3. An object is lifted vertically 6 meters and then returned to its original position. What was the work done on the object by gravity during the round trip if the object weighs 20 N? a) No work is done on the object b) 60 J c) 120 J d) 240 J e) -120 J 4. A sled is being pulled across a horizontal surface at a constant velocity. The pulling force is given by FA and is directed at an angle above the horizontal. What is the correct free-body diagram for the sled? Read the force labels carefully! FN FA (a) fs (b) fk FN FA (c) fk FN FA
W
W
W
FN FN (d) fs FA (e) fk FA
W
W
5. Two objects (3 kg and 9 kg) are released simultaneously on a frictionless inclined plane that makes an angle of 35o with the horizontal. What can we say about their accelerations after being released? a) The 3 kg object accelerates 3 times faster than the 9 kg object. b) The 9 kg object accelerates 3 times faster than the 3 kg object. c) Both objects accelerate at the same rate. d) none of the above.
6. A 3 kg object and a 9 kg object each experience the same, constant net force. Which of the following statements is true? a) The 3 kg object accelerates three times faster than the 9 kg object b) The 9 kg object accelerates three times faster than the 3 kg object c) Both objects accelerate at the same rate d) none of the above
7. Three balls are fired simultaneously with equal speeds from the same height above the ground. Ball 1 is fired straight down. Ball 2 is fired horizontally. Ball 3 is fired straight v3 up. Rank in order, from smallest to largest, their speeds as they hit the ground. (a) v1 < v2 < v3 (b) v1 < v3 < v2 (c) v2 < v1 < v3 (d) v2 > v3 < v1 (e) v1 = v2 = v3 v1
v2
8. A box is being pulled across a rough horizontal surface with an applied force FA at a constant velocity v. The normal force is FN , the kinetic frictional force is f K, and the weight of the box is W. Which forces are doing positive, zero, or negative work? FA (a) (b) (c) (d) (e) + + + + + fK + 0 W 0 0 0 FN 0 0 0 + 0
9. A rider in a barrel of fun finds herself stuck to the back of a wall as the barrel goes around in a circle and the bottom falls out. How many forces are acting on the woman? (a) Two Centripetal Force and Gravity (b) Two Friction and Gravity (c) Three - Friction, Gravity, and Force Normal (d) Four Centripetal Force, Friction, Gravity, and Normal Force (e) Five Centripetal Force, Friction, Gravity, Normal Force, and Tension
10. Two forces are acting on a small block. One of the forces is directed to the north and has magnitude 15 N. The other force has magnitude 25 N and is directed to the east. What is the magnitude of the net force on the block? a) 10 N b) 15 N c) 23 N d) 29 N e) 40 N
11. The mass of an object is a quantitative measure of (a) weight. (b) momentum. (c) force. (d) inertia. (e) acceleration.
12. A child starts from rest and slides down a frictionless slide of height 5.1 m. What is his speed when he hits the ground? (a) 5 m/s (b) 7 m/s (c) 10 m/s (d) 100 m/s (e) Cannot be solved need to know the child s mass, m
13. Which of the following is a long range force (so no contact is required)? (a) Gravitational Force (b) Normal Force (c) Frictional Force (d) Tension (e) Centripetal Force
14. The 1.9-kg toy car is moving on the track and approaching the loop, as shown. The track has a radius of 0.75 m. The car is moving at 6m/s at the instant shown. It stays in contact with the track as it goes through the loop. What is the free body diagram of the car at the highest point of the loop?
(a)
(b)
(c)
(d)
(e)
15. The 1.9-kg toy car is moving 2.57m/s at the highest point. The track has a radius of 0.75 m. What is the centripetal acceleration at the highest point? (a) (b) (c) (d) (e) 9.8 m/s2 8.8 m/s2 3.4 m/s2 48 m/s2 zero m/s2
16. After a box is given an initial push, it is sliding up an inclined plane that makes an angle of with respect to the horizontal. The coefficient of kinetic friction between the box and surface of the incline is given by k. The initial speed of the box at the bottom of the incline is given by v0 . How many forces are doing work (positive or negative) on the box? (a) One force (b) Two forces (c) Three forces (d) Four forces (e) No forces are doing work
v0 m 200
17. Does the tension acting on an object moving in a uniform circle do work on that object? a) Yes, since a force acts and the object moves, and work is force times distance. b) Yes, since it takes energy to turn an object. c) No, because the object has a constant speed. d) No, because the force and displacement of the object are always at right angles to one another.
18. Mike is cutting the grass using a human-powered lawn mower. He pushes the mower with a force of 45 N directed at an angle of 41 below the horizontal direction. How much work does Mike do on the mower in pushing it 9.1 m across the yard? a) No work is done on the mower b) 510 J c) 460 J d) 410 J e) 309 J
19. A 200 kg rock is sitting flat on the ground. A person who has a mass of 80 kg sits on the rock. What is the correct free body diagram for the rock? (a) (b) (c) (d) (e)
20. A 200 kg rock is sitting flat on the ground. A person who has a mass of 80 kg sits on the rock. What is the magnitude of the normal force exerted on the rock by the ground? a) 780 N b) 1180 N c) 1960 N d) 2740 N