Question

A horizontal massive platform is moving with a constant velocity $v_s$. At time $t=0$, a small block of mass $m$ is gently placed on the platform. If the coefficient of friction between the block and the platform is $\mu$ the work done by the force of friction on the block in the fixed ground reference frame (from $t=0$ to a sufficiently long time)is

• A. $+\frac{1}{2}m{v}_0^2$
• B. $-\frac{1}{2}m{v}_0^2$
• C. $+\frac{1}{2}\mu m{v}_0^2$
• D. $zero$

Answer 1

Answer: (A)

$+\frac{1}{2}m{v}_0^2$

$\begin{array}{c}\text{Correct option is}\left(A\right)\\ \text{Friction will act until the velocity of}\\ \text{small block is same as that of massive}\\ \text{bleck i.}e\text{.,}{V}_0\\ \begin{array}{c}\text{Work}=k_f-k_i\\ \text{Wfriction}=+\frac{1}{2}m{v}_0^2\end{array}\end{array}$