A ball is moving with 30J of kinetic energy,it then hits a boy in the face.The ball squashes by 2.5cm and has a spring constant of 50N/m, how much energy is transferred to the boy's face?

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Solution

Energy stored in ball when it squashes , $= \frac{1}{2} k x^{2} = \frac{1}{2} \times 50 \times (2.5 \times 10^{- 3})^{2} = 156.25 \times 10^{- 6} = 1.56 \times 10^{- 4} J$

Energy transferred to the boy's face = $30 - 1.56 \times 10^{- 4} J = 29.99 J$

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