Question:
A block of mass m is kept on a platform which starts from rest with constant acceleration g/2 upward, as shown in figure. Work done by normal reaction on block in time \(t\) is -
A block of mass m is kept on a platform which starts from rest with constant acceleration g/2 upward, as shown in figure. Work done by normal reaction on block in time \(t\) is -
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Find \(N\) from Newton's second law, the displacement \(s=\frac12 at^2\), and use \(W=Ns\).
Updated On: Nov 5, 2026
- \(\frac{mg^2t^2}{8}\)
- \(\frac{3mg^2t^2}{8}\)
- \(-\frac{mg^2t^2}{8}\)
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The Correct Option is B
Solution and Explanation
For the block: \(N - mg = m\cdot\frac g2\), so \(N = \frac{3mg}{2}\).
Displacement in time t from rest: \(s = \frac12\cdot\frac g2\cdot t^2 = \frac{gt^2}{4}\), upward (same direction as \(N\)).
\(W_N = N s = \frac{3mg}{2}\cdot\frac{gt^2}{4} = \frac{3mg^2t^2}{8}\).
Answer: (2) \(\frac{3mg^2t^2}{8}\)
Displacement in time t from rest: \(s = \frac12\cdot\frac g2\cdot t^2 = \frac{gt^2}{4}\), upward (same direction as \(N\)).
\(W_N = N s = \frac{3mg}{2}\cdot\frac{gt^2}{4} = \frac{3mg^2t^2}{8}\).
Answer: (2) \(\frac{3mg^2t^2}{8}\)
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