A plank is moving in a horizontal direction with a constant acceleration a i ^ . A uniform rough cubical block of side l rests on the plank and is at rest relative to the plank. Let the centre of mass of the block be at 0 , l / 2 at a given instant. If a = g / 10 , then the normal reaction exerted by the plank on the block at that instant acts at

Step-by-step solution

Given situation is Forces acting on the block are In above diagram, m a = pseudo force due to acceleration of plank, f = force of static friction, m g = weight of block and N = normal reaction. Here, we must note that due to motion of plank, normal reaction force does not passes through centre of mass. If line of action of normal force at a distance x from centre, then for equilibrium of block, net torque about centre of mass must be zero. ⇒ τ Normal reaction = τ Friction m g and m a does not produces any torque ab