A block whose weight is 40 N rests on a horizontal surface. The coefficient of static friction between the block and the surface is 0.50. A string is attached to the block. The string is pulled horizontally with a force of 15 N. Which one of the following statements is correct? The magnitude of the force of friction on the block is 5 N. The magnitude of the force of friction on the block is 15 N.     The force of friction cannot be determined because the coefficient of kinetic friction is not given. The magnitude of the force of friction on the block is 20 N. The force of friction cannot be determined because the normal force of the surface on the block is not known

A block whose weight is 40 N rests on a horizontal surface. The coefficient of static friction between the block and the surface is 0.50. A string is attached to the block. The string is pulled horizontally with a force of 15 N. Which one of the following statements is correct? The magnitude of the force of friction on the block is 5 N. The magnitude of the force of friction on the block is 15 N.     The force of friction cannot be determined because the coefficient of kinetic friction is not given. The magnitude of the force of friction on the block is 20 N. The force of friction cannot be determined because the normal force of the surface on the block is not known. 2. A block is sliding at constant speed down a ramp. Decide whether each of the following statements is true or false. (a) The net work done on the block as it slides equals zero. True or False     (b) The normal force does zero work on the block as it slides. True or False     (c) The friction force does positive work on the block as it slides. True or False     3. Two equal-mass balls, one blue and the other red, are dropped from the same height. Both balls bounce off the floor and rebound straight up. The rebounding blue ball reaches a greater height than the red ball. Which ball is subjected to a greater magnitude impulse during its collision with the floor? Both balls are subjected to the same magnitude impulse. The answer cannot be determined without knowing the time interval that each ball is in contact with the floor.     The red ball. The blue ball. 4. Two carts on a frictionless track are traveling directly toward each other. The first cart has mass m1 and speed v1, the second cart has mass m2 = (½)m1 and speed v2 = 2v1. If they collide head-on and stick together, what can you say about the total momentum and total kinetic energy of the two-cart system? Ignore friction and air resistance. ("final" refers to after the collision and "initial" refers to before the collision.) The final momentum equals the initial momentum and the final kinetic energy equals the initial kinetic energy. The final momentum is zero and the final kinetic energy equals the initial kinetic energy.     The final momentum is zero and the final kinetic energy equals half the initial kinetic energy The final momentum equals half the initial momentum and the final kinetic energy equals half the initial kinetic energy. The final momentum is zero and the final kinetic energy is zero. 5. A disk rotates about an axis through its center. Point A is located on its rim and point B is located exactly halfway from the center toward the rim. What is the ratio ?A/?B, of the angular velocity at A, ?A, to that of the angular velocity at B, ?B; and what is the ratio vtA/vtB, of the tangential velocity at A, vtA, to that of the tangential velocity at B, vtB? ?A/?B = 2 and vtA/vtB = 1 ?A/?B = 2 and vtA/vtB = 2     ?A/?B = 1 and vtA/vtB = 2 ?A/?B = ½ and vtA/vtB = 1 ?A/?B = 1 and vtA/vtB = 1 6. A motor increases its speed from 100 rev/min to 500 rev/min in 20 seconds. If this is done with a constant angular acceleration, how many revolutions occur in this 20 s interval? 100 rev 200 rev     6000 rev 170 rev 67 rev