1 NAME: FORM A PHYSICAL PRINCIPLES 1 EXAM 2 1. The block shown moves with constant velocity on a horizontal surface. Two of the forces on it are shown. A frictional force exerted by the surface is the only other horizontal force on the block. The frictional force is: A. 0 B. 2N, leftward C. 2N, rightward D. slightly more than 2N, leftward E. slightly less than 2N, leftward 2. A constant force of 8.0 N is exerted for 4.0 s on a 16-kg object initially at rest. The change in speed of this object will be: A. 0.5 m/s B. 2 m/s C. 4 m/s D. 8 m/s E. 32 m/s 3. A forward horizontal force of 12N is used to pull a 240-N crate at constant velocity across a horizontal floor. The coefficient of friction is: A. 0.5 B. 0.2 C. 2 D. 0.05 E. 20 2 4. Suppose that you must hold an object against a wall, such that it will not slip down. Which free-body diagram properly shows the forces acting on the object? (a) (b) (c) (d) (e) none of these 5. A 15 kg ball of wet clay drops off a workman’s scaffold and falls for 3.2 s before hitting the ground. If it comes to rest in 3 ms, what average force did the floor exert on the clay? (NOTE: 1 s = 1000 ms, 1 kN = 1000 N) (a) 157 N, (b) 147 kN, (c) 147 N, (d) 157 kN, (e) none of these 6. A ball is moving in a circle at a constant speed of 10 m/s counterclockwise. At one point the ball is moving straight North, as shown in the illustration below. At this point in time, what direction is the acceleration vector pointing? v = 10 m/s North North East (a) North, (b) South, (c) East, (d) West, (e) None of these 7. From question #6, at the same point in time, which direction does the velocity vector point? (a) North, (b) South, (c) East, (d) West, (e) NorthWest 3 8. The diagram shown below describes a force moving an object. What is the work done between from x = 0 to x = 7? (a) 1 J (b) 2 J (c) 9 J (d) 4 J (e) 10 J 2 Force (N) 0 4 6 7 Position (m) 9. An object of mass, m and velocity, v has kinetic energy, KE. What happens to the kinetic energy of the object if the velocity is doubled? (a) it stays the same (b) doubles (c) triples (d) quadruples (e) need more information 10. Two rocks, one three times as heavy as the other, are dropped to the ground from the roof of a building. Just before hitting the ground, the heavier object has (a) three times the velocity of the lighter rock (b) the same kinetic energy as the lighter rock (c) the same velocity of the lighter rock (d) four times the kinetic energy of the lighter rock (e) need more info 4 SHOW ALL YOUR WORK! NAME (7.5 POINTS) You are rotating a 4.5 kg ball on the end of a 1.5 m long string in a horizontal circle. The string makes an angle of 60º with respect to the horizontal, as shown in the illustration below. What is the speed of the ball? = 60º L = 1.5 m m = 4.5 kg 5 SHOW ALL YOUR WORK! NAME (7.5 POINTS) A hockey puck of mass m is attached to a string that passes through a hole in the center of a table, as shown below. The hockey puck moves in a circle of radius r. Tied to the other end of the string, and hanging vertically beneath the table, is a mass M. Assuming the tabletop is perfectly smooth, what speed must the hockey puck have if the mass M is to remain at rest?