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A stone weighing \( 5 kg \) falls from a height of \( 10 m \) on a long nail and drives through \( 4.9 cm \) in wooden board. Calculate K.E. of the stone when it just hits the nail and also the average retardation offered by the wooden board. \( \left(g=9.8 ms ^{-2}\right) \). |
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Answer» Given m = 5 kg h = 10 m s = 4.9 cm v2 = u2 + 2gh v2 = 0 + 2 x 9.8 x 10 v2 = 2 x 9.8 v = \(\sqrt{196}\) Then kinetic energy K.E. = \(\frac12mv^2\) = 1/2 x 5 x 196 K.E. = 490 J Retardation offered by the the wooden board v2 = u2 + 2 as 0 = (2 x 9.8 x 10) + (2 x a x 4.9 x 10-2) \(\frac{196}{9.8\times10^{-2}}=a\) a = 2000 m/s2 |
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