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TOPIC 4: Work, Energy and Power
When applying the Principle of Conservation of Energy, many students like to just apply the equation K.E. = P.E.
Although this may give the correct answer in simple problems, the precise form of the equation should be:
Gain in K.E = Loss in P.E. (for a falling object) ........ (1)
Loss in K.E. = Gain in P.E. (for a rising object) ........ (2)
For example, if an object initially travelling at 6m/s rolls down from the top to the bottom of a frictionless slope, and descends a vertical distance of 8m, what is its velocity at the bottom of the slope?
Using equation (1) above:
Gain in K.E = Loss in P.E.
½ m vbottom2 - ½ m vtop2 = mgh
½ m vbottom2 - ½ m (6)2 = m (10) (8)
½ vbottom2 - ½ (6)2 = (10) (8)
vbottom = 14 m s-1
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