Review 3: Forces. 1. Which graph best represents the motion of an object in equilibrium? A) B) C) D)

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1 1. Which graph best represents the motion of an object in equilibrium? A) B) C) D) 2. A rock is thrown straight up into the air. At the highest point of the rock's path, the magnitude of the net force acting on the rock is A) less than the magnitude of the rock's weight, but greater than zero B) greater than the magnitude of the rock's weight C) the same as the magnitude of the rock's weight D) zero 3. Which situation represents a person in equilibrium? A) a child gaining speed while sliding down a slide B) a woman accelerating upward in an elevator C) a man standing still on a bathroom scale D) a teenager driving around a corner in his car 4. A 750-newton person stands in an elevator that is accelerating downward. The upward force of the elevator floor on the person must be A) equal to 0 N B) less than 750 N C) equal to 750 N D) greater than 750 N 5. A 4.0-kilogram object is accelerated at 3.0 meters per second 2 north by an unbalanced force. The same unbalanced force acting on a 2.0-kilogram object will accelerate this object toward the north at A) 12 m/s 2 B) 6.0 m/s 2 C) 3.0 m/s 2 D) 1.5 m/s 2 6. At a certain location, a gravitational force with a magnitude of 350 newtons acts on a 70.-kilogram astronaut. What is the magnitude of the gravitational field strength at this location? A) 0.20 kg/n B) 5.0 N/kg C) 9.8 m/s 2 D) Nkg 7. An 8.0-newton wooden block slides across a horizontal wooden floor at constant velocity. What is the magnitude of the force of kinetic friction between the block and the floor? A) 2.4 N B) 3.4 N C) 8.0 N D) 27 N 8. An 80-kilogram skier slides on waxed skis along a horizontal surface of snow at constant velocity while pushing with his poles. What is the horizontal component of the force pushing him forward? A) 0.05 N B) 0.4 N C) 40 N D) 4N 9. The graph below shows the weight of three objects on planet X as a function of their mass. The acceleration due to gravity on planet X is A) 0.17 m/s 2 B) 6.0 m/s 2 C) 9.8 m/s 2 D) 50. m/s The diagram below shows a 4.0-kilogram object accelerating at 10. meters per second 2 on a rough horizontal surface. What is the magnitude of the frictional force Ff acting on the object? A) 5.0 N B) 10. N C) 20. N D) 40. N 11. A 0.50-kilogram puck sliding on a horizontal shuffleboard court is slowed to rest by a frictional force of 1.2 newtons. What is the coefficient of kinetic friction between the puck and the surface of the shuffleboard court? A) 0.24 B) 0.42 C) 0.60 D) Two 20.-newton forces act concurrently on an object. What angle between these forces will produce a resultant force with the greatest magnitude? A) 0º B) 45º C) 90.º D) 180.º

2 13.A kilogram boy and a 50.0-kilogram girl, each holding a spring scale, pull against each other as shown in the diagram below. The graph below shows the relationship between the magnitude of the force that the boy applies on his spring scale and time. Which graph best represents the relationship between the magnitude of the force that the girl applies on her spring scale and time? A) B) C) D)

3 14. Two forces act concurrently on an object on a horizontal, frictionless surface, as shown in the diagram below. What additional force, when applied to the object, will establish equilibrium? A) 16 N toward the right B) 16 N toward the left C) 4 N toward the right D) 4 N toward the left 15. In the diagram below, the upward drag force acting on a parachute is equal in magnitude but opposite in direction to the weight of the parachutist and equipment. 19. An 8.0-newton block is accelerating down a frictionless ramp inclined at 15 to the horizontal, as shown in the diagram below. What is the magnitude of the net force causing the block's acceleration? As a result of the forces shown, the parachutist may be moving A) downward with decreasing speed B) downward at constant speed C) upward with decreasing speed D) upward with constant acceleration 16. The diagram below shows a granite block being slid at constant speed across a horizontal concrete floor by a force parallel to the floor. A) 0 N B) 2.1 N C) 7.7 N D) 8.0 N 20. What force is required to push a block (mass m) up an inclined plane that makes an angle of q with the horizon at a constant velocity, if the coefficient of friction between the plane and the block is m? A) mg (m cos q + sin q ) B) mgm cos q C) mg (m sin q + cos q ) D) mg (m cos q + m sin q ) E) g (m cos q + m sin q ) 21. Base your answer to the following question on the picture below which shows a 3 kg block sliding 50 m down a frictionless inclined plane dropping a distance of 30 m. Which pair of quantities could be used to determine the coefficient of friction for the granite on the concrete? A) mass and speed of the block B) mass and normal force on the block C) frictional force and speed of the block D) frictional force and normal force on the block 17. A student wants to keep a block from falling down a frictionless ramp inclined at 53.1 degrees. If the block is to move at a constant rate how much force needs to be applied to a 50 newton block? A) 25 newtons B) 30 newtons C) 40 newtons D) 50 newtons E) 60 newtons 18. A 15 N force is applied to a 12 kg box for 6 s. The box is initially at rest. What is the speed of the box at the end of the 6 s interval? A) 1.8 m/s B) 3 m/s C) 7.5 m/s D) 15 m/s E) 30 m/s What is the magnitude of the normal force of the plane on the block? A) 5 N B) 8 N C) 16 N D) 24 N E) 30 N 22. A coin is dropped off the top of the Empire state building which is 440 meters high. The coin is kg if the coin encounters a constant resistant force of newtons. What is the acceleration of the coin when it lands? A) 5 m/s 2 B) 9 m/s 2 C) 10 m/s 2 D) 20 m/s 2 E) 30 m/s A 3 kg sled is pulled across a horizontal surface with a force of 30 N. The coefficient of friction between the surface and the sled is 0.2. What is the sled's acceleration? A) 4 m/s 2 B) 8 m/s 2 C) 10 m/s 2 D) 12 m/s 2 E) 15 m/s 2

4 24. A car is moving at 40 m/s. At 10 meters the driver spots a deer on the road and instantly steps on the brakes. If the car is 400 kg how much force must the brakes exert to stop the car in time? A) 0.5 newtons B) 80 newtons C) 160 newtons D) 3,200 newtons E) 32,000 newtons 25. A greased pig starts at rest from the top of a frictionless slide a height 25 m above his mud pit. If the bottom section of the slide is 5 m above the pit and is parallel to the ground, at what distance from the bottom of the slide will the pig hit the mud? A) 10 m B) 15 m C) 20 m D) 28 m E) 36 m 26. Base your answer to the following question on the following diagram, which shows a block that starts at the top of a frictionless ramp and slides down. If the mass of the block is 5 kg, how much work is done by gravity as the block slides down the full length of the incline? A) 10 J B) 100 J C) 200 J D) 1000 J E) 2000 J 27. The coefficient of kinetic friction between the highway and a car s tires are 0.1. The 3,000 newton car s tires lock up. How far will it skid if it was going 30 m/s? A) 0.2 meters B) 10.5 meters C) 45 meters D) 450 meters E) 5,000 meters 28. An object traveling at 16 m/s enters a frictional area. It comes to rest after a time of 4 s. The coefficient of friction of the frictional area is A) 0.3 B) 0.4 C) 0.5 D) 0.9 E) 1.6

5 Answer Key Review 3 1. A 2. C 3. C 4. B 5. B 6. B 7. A 8. C 9. B 10. B 11. A 12. A 13. A 14. D 15. B 16. D 17. C 18. C 19. B 20. A 21. D 22. B 23. B 24. E 25. C 26. D 27. D 28. B