20.Gravinational potential energy is (a)independent of vertical position , y, (b

Question

20.Gravinational potential energy is (a)independent of vertical position , y, (b) is always positive (c) independent of mass , m, (d)none of the preceding. 21. The position or reference point for zero gravitational potential energy. (a) must always be at ground level, (b) depends on an object's position, (C) is arbitrary(we are free to chose). (d) cannot be negative. 22. A rock of mass m is dropped to the ground from a height h. A second rock, with 3m, is dropped from the same height. When the second rock strikes the ground, which of the following best describes its kinetic) energy? (a) nine times that of the first rock (b) the same as that of the first rock lc) thrice that of the first rock Id) impossible to determine (e) one-third as much as that of the first rock 23. Three identical balls are thrown from the t.1, of a building all with the same initial speed. The first is thrown horizontally, the second at some angle above the horizontal, and the third at some angle below the horizontal, as shown below. Neglecting air resistance, rank the speeds of the the balls just before they hit the grounds. 24. Power (a) is work times time, (b) has the unit of joules, (C) is independent of efficiency, (d) is the time rate of doing work. 25. A 1.0 hp engine compared to a .50 hp engine can do twice the work in (a) the same time, (b) one - half the time. (C) twice the time. (d) none of the preceding

Explanation / Answer

20)d

21)c

22)c

23)1<2=3

24)d

25)a

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