Question

A massive platform of mass M is moving with speed v=6 ms^-1. At t=0 a body of mass m (m << M) is gently placed on the platform. If coefficient of friction between body and platform is μ = 0.3 and g = 10 m/s². Then

• A. The body covers a distance 3 m on the platform in the direction of motion of the platform.
• B. The body covers a distance 3 m on the platform opposite to the direction of motion of platform before coming to rest.
• C. The body covers a distance 6 m on the platform in the direction of motion of the platform.
• D. The body covers a distance 6 m on the platform opposite to the direction of motion of platform before coming to rest.

Answer 1

Answer: (D)

The body covers a distance 6 m on the platform opposite to the direction of motion of platform before coming to rest.

Answer 2

Since M>>m, the velocity of M remains unchanged after m is placed on to it.

Acceleration of m, a = $\frac{\mu mg}{m}$ = μg

a_mM = a - 0 = a and initial relative velocity v_mM = 0 - v = -v

Hence s = $\frac{v^{2}}{2\mu g} = \frac{6^{2}}{2 \times 0.3 \times 10}$ = 6 m Hence the correct choice is