Q. 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 bv normal reaction on block in time t is :

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Solution:

$N- mg = \frac{mg}{2} \Rightarrow N = \frac{3mg}{2} $
Now, work done $ W =\vec{N} \vec{S} =\left(\frac{3mg}{2}\right)\left(\frac{1}{2} gt^{2}\right) $
$ \Rightarrow W = \frac{3mg^{2}t^{2}}{4} $

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