Practice Test for Midterm Exam

Transcription

1 A.P. Physics Practice Test for Midterm Exam Kinematics 1. Which of the following statements are about uniformly accelerated motion? Select two answers. a) If an object s acceleration is constant then it must move in a straight line. b\ If an object s acceleration is zero, then it s speed must remain constant. c) If an object s speed remains constant, then its acceleration must be zero. d\ If the object s direction of motion is changing then its acceleration is not zero. 2. How long would it take a car, starting from rest and accelerating uniformly in a straight line at 5 m/s 2, to cover a distance of 200 m? a\ 9.0 s c) 12.0 s b) 10.5 s d) 15.5 s 3. A stone is thrown horizontally with an initial speed of 30 m/s from a bridge. Find the stone s total speed when it enters the water 4 seconds later. (Ignore air resistance.) a) 30 m/s c\ 50 m/s b) 40 m/s d) 60 m/s 4. A soccer ball, at rest on the ground, is kicked with an initial velocity of 10 m/s at a launch angle of 30. Calculate its total flight time, assuming that air resistance is negligible. Name Period Date / / 5. Which one of the following statements is true concerning the motion of an ideal projectile launched at an angle of 45 to the horizontal? a) The acceleration vector points opposite to the velocity vector on the way up and in the same direction as the velocity vector on the way down. b) The speed at the top of the trajectory is zero. c) The object s total speed remains constant during the entire flight. d\ The vertical speed decreases on the way up and increases on the way down. * * * * * * * * * * * * * * * * * * * * * Newton s Laws 6. A person standing on a horizontal floor feels two forces: the downward pull of gravity and the upward supporting force from the floor. These two forces a) have equal magnitudes and form an action/reaction pair. b\ have equal magnitudes but do not form an action/reaction pair. c) have unequal magnitudes and form an action/reaction pair. d) have unequal magnitudes and do not form an action/reaction pair. a) 0.5 s c) 2 s b\ 1 s d) 4 s

2 7. A person who weighs 800 N steps onto a scale that is on the floor of an elevator car. If the elevator accelerates upward at a rate of 5 m/s 2, what will the scale read? 11. Assuming a frictionless, mass-less pulley, determine the acceleration of the blocks once they are released from rest. a) 400 N c) 1000 N b) 800 N d\ 1200 N 8. A frictionless inclined plane of length 20 m has a maximum vertical height of 5 m. If an object of mass 2 kg is placed on the plane, which of the following best approximates the net force it feels? a\ 5 N c) 15 N b) 10 N d) 20 N 9. A 20 N block is being pushed across a horizontal table by an 18 N force. If the coefficient of kinetic friction between the block and the table is 0.4, find the acceleration of the block. a) 0.5 m/s 2 c\ 5 m/s 2 b) 1 m/s 2 d) 7.5 m/s 2 m a) m g M + m b) M g m c) (M + m) g (M m) d\ (M m) g (M + m) M 10. The coefficient of static friction between a box and a ramp is 0.5. The ramp s incline angle is 30. If the box is placed at rest on the ramp, the box will do which of the following? a\ Accelerate down the ramp. b) Accelerate briefly down the ramp but then slow down and stop. 12. If all of the forces acting on an object balance so that the net force is zero, then a) the object must be at rest. b) the object s speed will decrease. c) the object s direction of motion can change, but not its speed. d\ None of the above will occur. c) Move with constant velocity down the ramp. d) Not move.

3 13. A block of mass m is at rest on a frictionless, horizontal table placed in a laboratory on the surface of the Earth. An identical block is at rest on a frictionless horizontal table placed on the surface of the Moon. Let F be the net force necessary to give the Earth bound block an acceleration of a across the table. Given that g Moon is one-sixth of g Earth, the force necessary to give the Moon bound block the same acceleration a across the table is a) F/6 c\ F b) F/3 d) 6 F * * * * * * * * * * * * * * * * * * * * * Work, Energy and Power 14. A force F of strength 20 N acts on an object of mass 3 kg as it moves a distance of 4 m. If F is perpendicular to the 4 m displacement, the work it does is equal to a\ 0 J c) 80 J b) 60 J d) 600 J 15. Under the influence of a force, an object of mass 4 kg accelerates from 3 m/s to 6 m/s in 8 s. How much work was done on the object during this time? a) 27 J c) 72 J b\ 54 J d) 96 J 16. A box of mass m slides down a frictionless inclined plane of length L and vertical height h. What is the change in its gravitational potential energy? 17. While a person lifts a book of mass 2 kg from the floor to a tabletop, 1.5 m above the floor, how much work does the gravitational force do on the book? a\ 30 J c) 0 J b) 15 J d) 15 J 18. A block of mass 3.5 kg slides down a frictionless inclined plane of length 6.4 m that makes an angle of 30 with the horizontal. If the block is released from rest at the top of the incline, what is its speed at the bottom? a) 5.0 m/s c\ 8.0 m/s b) 6.4 m/s d) 10 m/s 19. An astronaut drops a rock from the top of a crater on the Moon. When the rock is halfway down to the bottom of the crater, its speed is what fraction of its final impact speed? a) 1/4 c) 1/2 b) 1/2 2 d\ 1/ A force of 200 N is required to keep an object sliding at a constant speed of 2 m/s across a rough floor. How much power is being expended to maintain this motion? a) 50 W c) 200 W b) 100 W d\ 400 W a) m g L c) m g L/h b\ m g h d) m g h/l

4 Uniform Circular Motion and Gravitation 21. An object moves at constant speed in a circular path. Which of the following statements is true? (Select two answers) a\ The velocity is changing b) The velocity is constant. c\ The magnitude of acceleration is constant. d) The magnitude of acceleration is changing. 24. An object moves at a constant speed in a circular path of radius r at a rate of 1 revolution per second. What is its acceleration? a) 0 c) 2π 2 r b) 2π 2 r 2 d\ 4π 2 r 25. If the distance between two point particles is doubled, then the gravitational force between them a\ decreases by a factor of 4 b) decreases by a factor of 2 c) increases by a factor of 2 Questions 22 23: A 60 cm rope is tied to the handle of a bucket which is then whirled in a vertical circle. The mass of the bucket is 3 kg. 22. At the lowest point in its path, the tension in the rope is 50 N. What is the speed of the bucket? (Hint: 1 st find net force) a) 1 m/s c) 3 m/s b\ 2 m/s d) 4 m/s d) increases by a factor of At the surface of Earth, an object of mass m has a weight w. If this object is transported to an altitude that is twice the radius of Earth, then at the new location, a) its mass is m and its weight is w/2 b) its mass is m/2 and its weight is w/4 c) its mass is m and its weight is w/4 d\ its mass is m and its weight is w/9 23. What is the critical speed below which the rope would become slack when the bucket reaches the highest point in the circle? (Hint: Which force becomes zero when the rope becomes slack?) a) 0.6 m/s c\ 2.4 m/s b) 1.8 m/s d) 4.8 m/s 27. A moon of mass m orbits a planet of mass 100 m. Let the strength of the gravitational force exerted by the planet on the moon be denoted by F 1, and let the strength of the gravitational force exerted by the moon on the planet be F 2. Which of the following is true? a) F 1 = 100 F 2 c\ F 1 = F 2 b) F 1 = 10 F 2 d) F 2 = 10 F 2

5 28. The dwarf planet Pluto has 1/500 the mass and 1/15 the radius of Earth. What is the value of g (in m/s 2 ) on the surface of Pluto? a) 50/225 c) 15/50 b) 50/15 d\ 225/ You are looking at a top view of a planet orbiting the Sun in a clockwise direction. Which of the following would describe the velocity, acceleration, and force acting on the planet due to the Sun s pull at point P? 31. An object of mass m is traveling at constant speed v in a circular path of radius r. How much work is done by the centripetal force during one-half of a revolution? a) π m v 2 c) π m v 2 r b\ 0 d) 2 π m v 2 r Linear Momentum 32. An object of mass 2 kg has a linear momentum of magnitude 6 kg m/s. What is the object s kinetic energy? Sun P a) 3 J c\ 9 J b) 6 J d) 12 J a) v a F b\ v a F c) v a F d) v a F 33. A ball of mass 0.5 kg, initially at rest, acquires a speed of 4 m/s immediately after being kicked by a force of strength 20 N. For how long did this force act on the ball? a) 0.01 s c) 0.2 s b\ 0.1 s d) 1 s 30. Which of the following statements are true for a satellite in outer space orbiting the Earth in uniform circular motion? Select two answers. a) There are no forces acting on the satellite. b\ The force of gravity is the only force acting on the satellite. c) The force of gravity is balanced by outward forces of the object. 34. A box with a mass of 2 kg accelerates in a straight line from 4 m/s to 8 m/s due to the application of a force whose duration is 0.5 seconds. Find the average strength of this force. a\ 4 N c) 12 N b) 8 N d\ 16 N d\ The mass of the satellite has no effect on the orbital speed.

6 35. A ball of mass m traveling horizontally with velocity v strikes a massive vertical wall and rebounds back along its original direction with no change in speed. What is the magnitude of the impulse delivered by the wall to the ball? a) ½ m v c\ 2 m v b) m v d) 4 m v 38. Two frictionless carts (mass = 500 g each) are sitting at rest on a perfectly level table. The teacher taps the release so that one cart pushes off the other. If one of the carts has a speed of 2 m/s, then what is the final momentum of the system (in kg m/s)? a) 2000 c) 2 b) 1000 d\ Two objects, one of mass 3 kg and moving with a speed of 2 m/s and the other of mass 5 kg and speed 2 m/s, move toward each other and collide head on. If the collision is perfectly inelastic, find the speed of the objects after the collision. a) 0.25 m/s c) 0.75 m/s b\ 0.5 m/s d) 1 m/s 39. Which of the following best describes a perfectly inelastic collision free of external forces? a) Total linear momentum is never conserved. b) Total linear momentum is sometimes conserved. c\ Kinetic energy is never conserved. d) Kinetic energy is always conserved. 37. Two objects move toward each other, collide, and separate. If there was no net external force acting on the objects, but some kinetic energy was lost, then a) the collision was elastic and total linear momentum was conserved. b) the collision was elastic and total linear momentum was not conserved. c\ the collision was not elastic and total linear momentum was conserved. d) the collision was not elastic and total linear momentum was not conserved. 40. A wooden block of mass M is moving at speed V in a straight line. m How fast would the bullet of mass m need to travel to stop the block (assuming that the bullet became imbedded inside)? (Hint: their combined momentum after impact should be zero) V M a) mv / (m + M) c\ M V / m b) mv / M d) (m + M) V/ m

7 A.P. Physics Practice Test for Midterm Exam (Answers) ANSWERS 1. B, D 11. D 21. A, C 31. B 2. A 12. D 22. B 32. C 3. C 13. C 23. C 33. B 4. B 14. A 24. D 34. A 5. D 15. B 25. A 35. C 6. B 16. B 26. D 36. B 7. D 17. A 27. C 37. C 8. A 18. C 28. D 38. D 9. C 19. D 29. B 39. C 10. A 20. D 30. B, D 40. C