(New tips are continually added to these pages.  Check back in a few months' time for more)

TOPIC 4:     Work, Energy and Power

Tip 1:

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 v_bottom² - ½ m v_top² = mgh

½ m v_bottom² - ½ m (6)² = m (10) (8)

½ v_bottom² - ½ (6)² = (10) (8)

v_bottom = 14 m s^-1

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