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13. Jill does twice as much work as Jack does and in half the time. Jill's power output is A) the same as Jack's power output. B) one-fourth as much as Jack's power output. C) one-half as much as Jack's power output. D) twice Jack's power output. E) four times Jack's power output. 14. It requires 0.30 kJ of work to fully drive a stake into the ground. If the average resistive force on the stake by the ground is 828 N, how long is the stake? A) 0.36 m B) 0.23 m C) 0.31 m D) 0.41 m 15. A rock falls from a vertical cliff that is 4.0 m tall and experiences no significant air resistance as it falls. At what speed will its gravitational potential energy (relative to the base of the cliff) be equal to its kinetic energy? A) 3.1 m/s B) 4.4 m/s C) 6.3 m/s D) 8.9 m/s E) 13 m/s 16. A 1500-kg car accelerates from rest to 25 m/s in 7.0 s. What is the average power delivered by the engine? (1 hp = 746 W) A) 60 hp B) 70 hp C) 80 hp D) 90 hp 17. A 20-ton truck collides with a 1500-lb car and causes a lot of damage to the car. During the collision A) the force on the car due to the collision is much greater than the force on the truck B) the force on the truck due to the collision is slightly greater than the force on the car. C) the car and the truck have the same magnitude acceleration. D) the force on the truck due to the collision is exactly equal to the force on the car. 18. The momentum of an isolated system is conserved A) only in inelastic collisions. B) only in elastic collisions. C) in both elastic and inelastic collisions. 19. A 328-kg car moving at 19.1 m/s in the +x direction hits from behind a second car moving at 130m/s in the same direction. If the second car has a mass of 790 kg and a speed of 151m/'s right after the collision, what is the velocity of the first car after this sudden collision? A) 14.0 m/s B) 18.2 m/s C) 24.2 m/s D) -14.0 m/s 20. A golf club exerts an average horizontal force of 1000 N on a 0.045-kg golf ball that is initially at rest on the tee. The club is in contact with the ball for 1.8 ms. What is the speed of the golf ball just as it leaves the tee? A) 30 m/s B) 35 m/s C) 40 m/s D) 45 m/s E) 50 m/s