Physics 125 Practice Exam #3 Chapters 6-7 Professor Siegel

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1 Physics 125 Practice Exam #3 Chapters 6-7 Professor Siegel Name: Lab Day: 1. A concrete block is pulled 7.0 m across a frictionless surface by means of a rope. The tension in the rope is 40 N; and the net work done on the block is 247 J. What angle does the rope make with the horizontal? A) 28 B) 41 C) 47 D) 62 E) A constant force of 25 N is applied as shown to a block which undergoes a displacement of 7.5 m to the right along a frictionless surface while the force acts. What is the work done by the force? A) zero joules B) +94 J C) 94 J D) +160 J E) 160 J Page 1

2 3. A 1.0-kg ball on the end of a string is whirled at a constant speed of 2.0 m/s in a horizontal circle of radius 1.5 m. What is the work done by the centripetal force during one revolution? A) zero joules B) 2.7 J C) 6.0 J D) 25 J E) 33 J 4. Which one of the following statements concerning kinetic energy is true? A) Kinetic energy can be measured in watts. B) Kinetic energy is always equal to the potential energy. C) Kinetic energy is always positive. D) Kinetic energy is a quantitative measure of inertia. E) Kinetic energy is directly proportional to velocity. 5. How much energy is dissipated in braking a 1200-kg car to a stop from an initial speed of 30 m/s? A) J B) J C) J D) J E) J 6. A 10.0-g bullet traveling horizontally at 755 m/s strikes a stationary target and stops after penetrating 14.5 cm into the target. What is the average force of the target on the bullet? A) N B) N C) N D) N E) N 7. Use the work-energy theorem to find the force required to accelerate an electron (m = kg) moving along the x axis from m/s to m/s in a distance of m. A) N B) N C) N D) N E) N Page 2

3 8. A helicopter (m = 3250 kg) is cruising at a speed of 56.9 m/s at an altitude of 185 m. What is the total mechanical energy of the helicopter? A) J B) J C) J D) J E) J 9. A pebble rolls off the roof of Science Hall and falls vertically. Just before it reaches the ground, the pebble's speed is 17 m/s. Neglect air resistance and determine the height of Science Hall. A) 42 m B) 33 m C) 26 m D) 21 m E) 15 m 10. Two boxes are connected to each other as shown. The system is released from rest and the 1.00-kg box falls through a distance of 1.00 m. The surface of the table is frictionless. What is the kinetic energy of box B just before it reaches the floor? A) 2.45 J B) 4.90 J C) 9.80 J D) 29.4 J E) 39.2 J Page 3

4 11. A physics student shoves a 0.50-kg block from the bottom of a frictionless 30.0 inclined plane. The student performs 4.0 J of work and the block slides a distance s along the incline before it stops. Determine the value of s. A) 8.0 cm B) 16 cm C) 82 cm D) 160 cm E) 330 cm 12. The initial velocity of a 4.0-kg box is 11 m/s, due west. After the box slides 4.0 m horizontally, its speed is 1.5 m/s. Determine the magnitude and the direction of the nonconservative force acting on the box as it slides. A) 42 N, due west B) 120 N, due east C) 31 N, due east D) 59 N, due east E) 83 N, due west 13. An automobile approaches a barrier at a speed of 20 m/s along a level road. The driver locks the brakes at a distance of 50 m from the barrier. What minimum coefficient of kinetic friction is required to stop the automobile before it hits the barrier? A) 0.4 B) 0.5 C) 0.6 D) 0.7 E) What power is needed to lift a 49-kg person a vertical distance of 5.0 m in 20.0 s? A) 12.5 W B) 25 W C) 60 W D) 120 W E) 210 W Page 4

5 15. Jennifer is walking at 1.22 m/s. If Jennifer weighs 552 N, what is the magnitude of her momentum? A) 97.0 kg m/s B) 137 kg m/s C) 68.6 kg m/s D) 672 kg m/s E) 951 kg m/s 16. A 1.0-kg ball has a velocity of 12 m/s downward just before it strikes the ground and bounces up with a velocity of 12 m/s upward. What is the change in momentum of the ball? A) zero kg m/s B) 12 kg m/s, downward C) 12 kg m/s, upward D) 24 kg m/s, downward E) 24 kg m/s, upward 17. A stationary bomb explodes in space breaking into a number of small fragments. At the location of the explosion, the net force due to gravity is zero newtons. Which one of the following statements concerning this event is true? A) Kinetic energy is conserved in this process. B) All of the fragments must have equal kinetic energies. C) The sum of the kinetic energies of the fragments must be zero. D) The vector sum of the linear momenta of the fragments must be zero. E) The mass of any one fragment must be equal to the mass of any other fragment. 18. A 100-kg cannon at rest contains a 10-kg cannon ball. When fired, the cannon ball leaves the cannon with a speed of 90 m/s. What is the recoil speed of the cannon? A) 4.5 m/s B) 9 m/s C) 45 m/s D) 90 m/s E) zero m/s 19. Complete the following statement: Different types of collisions between interacting bodies are categorized on the basis of A) kinetic energy conservation. B) mechanical energy conservation. C) linear momentum conservation. D) the magnitude of the forces involved. E) the temporal duration of the collision. Page 5

6 20. Complete the following statement: A collision is elastic if A) the final velocities are zero. B) the objects stick together. C) the final kinetic energy is zero. D) the final momentum is zero. E) the total kinetic energy is conserved. 21. A 3.0-kg cart moving to the right with a speed of 1.0 m/s has a head-on collision with a 5.0-kg cart that is initially moving to the left with a speed of 2.0 m/s. After the collision, the 3.0-kg cart is moving to the left with a speed of 1.0 m/s. What is the final velocity of the 5.0-kg cart? A) zero m/s B) 0.80 m/s to the right C) 0.80 m/s to the left D) 2.0 m/s to the right E) 2.0 m/s to the left 22. A kg lump of clay moving horizontally at 12 m/s strikes and sticks to a stationary 0.15-kg cart that can move on a frictionless air track. Determine the speed of the cart and clay after the collision. A) zero m/s B) 3 m/s C) 6 m/s D) 9 m/s E) 12 m/s 23. A 50.0-kg boy runs at a speed of 10.0 m/s and jumps onto a cart as shown in the figure. The cart is initially at rest. If the speed of the cart with the boy on it is 2.50 m/s, what is the mass of the cart? A) 150 kg B) 175 kg C) 210 kg D) 260 kg E) 300 kg Page 6

7 24. A 0.10-kg cart traveling in the positive x direction at 10.0 m/s collides with a 0.30-kg cart at rest. The collision is elastic. What is the velocity of the 0.10-kg cart after the collision? A) +2.5 m/s B) 2.5 m/s C) +5 m/s D) 5 m/s E) +3.3 m/s Use the following to answer question 25: A stationary 4-kg shell explodes into three pieces. Two of the fragments have a mass of 1 kg each and move along the paths shown with a speed of 10 m/s. The third fragment moves upward as shown. 25. What is the speed of the third fragment? A) zero m/s B) 1 m/s C) 5 m/s D) 10 m/s E) 20 m/s Page 7

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