KVPY SX SB Exam 2018 Question Paper

Question : 28 of 120

Marks: +1, -0

A plank is moving in a horizontal direction with a constant acceleration ˆ ai . A uniform rough cubical block of side l rests on the plank, and is at rest relative to the plank.

Let the center of mass of the block be at (0, l/2) at a given instant. If a = g/10, then the normal reactionexerted by the plank on the block at that instant acts at

(0, 0)
(–l/20, 0)
(–l/10, 0)
(l/10, 0)

Validate

Solution:

Torque balance about com of block

Nx = fr l/2

Nx = mal/2

Nx = {mg}/10×l/2

x=l/20

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