WAEC - Physics (2008 - No. 15)
An object of mass 0.25kg moves at a height h above the ground with a speed of 4ms-1, if its mechanical energy at this height is 12 J, determine the value of h. [g = 10ms-1]
0.8m
4.0m
4.8m
5.6m
Explanation
The total mechanical energy E at height h is given by: E = PE + KE
E = mgh + \(\frac{1}{2}\)mv\(^2\)
12 = (0.25 x 10 x h) + (0.5 x 0.25 x 4 x 4)
12 = 2.5h + 2
2.5h = 12 - 2 = 10
h = \(\frac{10}{2.5}\) = 4m.
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