JEE Main201910 Jan 2019Morning ShiftPhysicsLaws of MotionActual
A block of mass m is kept on a platform which starts from rest with a constant acceleration g / 2 upwards, as shown in the figure. Work done by normal reaction on block in time t is
Options
- A- m g 2 t 2 8
- Bm g 2 t 2 8
- C0
- D3 m g 2 t 2 8
Correct answer
D. 3 m g 2 t 2 8
Step-by-step solution
N - m g = m g 2 N = 3 m g 2 s = u t + 1 2 a t 2 = 0 + 1 2 g 2 t 2 = g 4 t 2 W N = 3 m g 2 × g 4   t 2 = 3 m g 2 t 2 8 = 3 m g 2 t 2 8