1. A boy throws a ball vertically upwards from ground level. If the ball reaches a maximum height of 250 m and the gravitational acceleration is 9.8 m/s2, with what speed did the boy throw the ball?   35 m/s   70 m/s   50 m/s   10 m/s   Hint Half-n-half Clue   2. The energy acquired by a body because of its motion is called potential energy.   True   False   3. Efficiency of a machine equals   Work Input / Work Output × 100 %   Work Output / Work Input × 100 %   Work Input / (Work Input + Work Output) × 100 %   Work Output / (Work Input + Work Output) × 100 %   Half-n-half Clue   4. A body loses 2940 J of potential energy in falling through 50 m. If the gravitational acceleration is 9.8 m s-2, then the body has a mass of   59 kg   300 kg   6 kg   490 kg   Half-n-half Clue   5. The energy losses from machines are mostly dissipated as sound energy.   True   False   6. If there is no friction, the efficiency of a machine can be greater than 100 %.   True   False   7. If an engine does 592 J of work in 8 seconds, its average power is   4736 W   584 W   74 W   600 W   Half-n-half Clue