Question

A block of mass M is placed on the top of a wedge of mass 4M. All the surfaces are frictionless. The system is released from rest. The distance moved by the wedge at the instant the block reaches the bottom will be :

• A. $0.2m$
• B. $0.4m$
• C. $0.8m$
• D. $0m$

Answer 1

Answer: (C)

$0.8m$

If $x$ be the distance moved by the wedge of mass $4M$ at instant

when block $M$ reaches at the bottom, then block $M$ also move

$(4-x)$ distance at that instant.

Therefore, $4Mx=M(4-x)$ (as work done by block $M$ is equal to the

work done by wedge of mass $4M$)

$\Rightarrow 5Mx=4M$

$\Rightarrow x=\frac{4}{5}=0.8m$