1. If an engine does 960 J of work in 10 seconds, its average power is   96 W   950 W   9600 W   970 W   Hint Half-n-half Clue   2. A body loses 7938 J of potential energy in falling through 90 m. If the gravitational acceleration is 9.8 m s-2, then the body has a mass of   9 kg   810 kg   88 kg   882 kg   Half-n-half Clue   3. Efficiency of a machine equals   Work Input / Work Output × 100 %   Work Output / (Work Input + Work Output) × 100 %   Work Input / (Work Input + Work Output) × 100 %   Work Output / Work Input × 100 %   Half-n-half Clue   4. If there is no friction, the efficiency of a machine can be greater than 100 %.   True   False   5. The maximum amount of work that can be done by a 30 kW machine in 8 seconds is   4 J   240 J   4 kJ   240 kJ   Half-n-half Clue   6. Both work and heat are measured in Joules.   True   False   7. A machine that produces 104 J of work by using 160 J of energy has an efficiency of   35 %   56 J   65 %   13 J   Half-n-half Clue