1. Power is the rate of doing work.   True   False   2. 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?   50 m/s   35 m/s   10 m/s   70 m/s   Hint Half-n-half Clue   3. A pebble is dropped from the top of a cliff 84 m in height. The kinetic energy of the pebble equals twice its potential energy at a distance of _______ above sea level.   28 m   42 m   21 m   63 m   Half-n-half Clue   4. The SI unit of power is   Joule   Volt   Watt   Half-n-half Clue   5. A mass of 100 kg is moved vertically upwards through a distance of 2 m. If the gravitational acceleration is 9.8 m s-2, then the work done against gravity is   200 J   980 J   1960 J   19.6 J   Half-n-half Clue   6. A body loses 1470 J of potential energy in falling through 30 m. If the gravitational acceleration is 9.8 m s-2, then the body has a mass of   294 kg   150 kg   49 kg   5 kg   Half-n-half Clue   7. If an engine does 679 J of work in 7 seconds, its average power is   686 W   672 W   97 W   4753 W   Half-n-half Clue