Which of the following statements are true? (Select all that apply.) Work done b

Question

Which of the following statements are true? (Select all that apply.) Work done by frictional forces must always decrease the total mechanical energy of a system. Compressing a glven spring 2.0 cm from its unstressed length takes more work than stretching It 2.0 cm from its unstressed length None of these statements are true. When you jump Into the alr, the floor does work on you, Increasing your mechanical energy The total energy of a system cannot change eBook My Notes OAsk Your Teacher 10. +-/1 points Tipler6 7P020 Water flows over VIctorla Falls, which Is 128 m hlgh, at an average rate or 1.30 x 106 Kg/s. I one quarter the potential energy of this water were converted to electric energy, how much power would be produced by these falls? MW eBook

Explanation / Answer

(1)

a) False - work done by friction forces is not always -ve. so always not decreases the total mechanical energy.

eg -  frictional force that accelerates a sprinter increases the total mechanical energy of the sprinter

b)

False

W = (1/2)kx^2

work done is same for both cases whether spring is streched or compress

(d)

False - when you jump in the air floor does work and increases energ

(e)

False - total energy of system can change if external forces are working on system

None of these statements are true.

(10)

potential energy of water per second,

E = (m / T )*gh = 1.30*10^6*9.8*128

E = 1630.72*10^6 J/s

one quarter of this PE is converted to electrical energy.

Power = (1/4)*E

P = 407.68 MW

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