8. (A) If the amount of friction present in a moving machine decreases, a. the energy lost to heat decreases and the percent efficiency decreases. b. the energy lost to heat decreases and the percent efficiency increases. c. the energy lost to heat increases and the percent efficiency decreases. d. the energy lost to heat increases and the percent efficiency increases. 9. (K) The force that ultimately lifts a basketball player upwards off the court in a slam- dunk jump is the: a. applied force b. tension c. torque d. normal force 10. (A) A boy on a swing is pulled to a position 2.34 m off the ground and released. At the fastest and lowest point of the swing the boy is 0.50 m off the ground and travelling 3 m/s. The percent efficiency of this swing system is: a. 10% b. 25% c. 50% d. 70% 11. (K) If a 1.5 kg chicken is running with a speed of 10.0 m/s, its kinetic energy is: a. 150 J b. 7.5 J c. 75 J d. 6.7 J 12. (A) A ball is dropped from a height of 3.0 m. As it falls a. its gravitational potential energy increases and its kinetic energy increases. b. its gravitational potential energy increases and its kinetic energy decreases. c. its gravitational potential energy decreases and its kinetic energy increases. d. its gravitational potential energy decreases and its kinetic energy decreases. 13.(A) If done long enough, rubbing two sticks together can produce enough work to start a fire. If 100.0 J of thermal energy is required to start the fire and the average frictional force between the sticks is 20.0 N, the distance the sticks must slide past one other is: a. 2.00 m b. 5.00 m c. 10.0 m d. 100.0 m 14. (K) The amount of energy used by a 100 W light bulb in 1 minute is: a. 6000 J b. 100 J c. 600 J d. 1.7 J e. 60 000 J 15. (A) Which of the following energy transformations best describes the operation of a battery powered flashlight? a. electrical energy -> thermal energy -> kinetic energy b. thermal energy -> elastic potential energy -> electrical energy c. radiant energy -> electrical energy -> chemical potential energy d. chemical energy -> electrical energy -> radiant energy