A block of mass m is kept on a platform which starts from rest with constant acceleration g/2 upward, as shown in fig. Work done by normal reaction on block in time t is :

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$\frac{{mg}^{2} t^{2}}{8}$

$- \frac{{mg}^{2} t^{2}}{8}$

$\frac{3 {mg}^{2} t^{2}}{8}$

answer is D.

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Detailed Solution

Here, N-mg $= ma = \frac{mg}{2}$

$\Rightarrow N = \frac{3 mg}{2} here N = normal reaction$
Now, work done by normal reaction ‘N’ on block in time t,
$W = \vec{N} \vec{S} = (\frac{3 mg}{2}) (\frac{1}{2} g / 2) t^{2} Or, W = \frac{3 {mg}^{2} t^{2}}{8}$

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