Question

A small block of mass $m$ is kept on a rough inclined surface of inclination $\theta$ fixed in an elevator. The elevator goes up with a uniform velocity $v$ and the block does not slide on the wedge. The work done by the force of friction on the block in time $t$ as seen by the observer on the inclined plane will be :

• A. zero
• B. $mgvt{\cos }^2\theta$
• C. $mgvt{\sin }^2\theta$
• D. $mgvt\sin 2\theta$

Answer 1

Answer: (A)

zero

Work done by friction force $W=fS\cos \theta$

where $f$ is the friction force , $S$ is the displacement of the block and $\theta$ is the angle between $f$ and $S$.

Since the block does not slide on the wedge, so the displacement of the block w.r.t the observer on an incline will be zero. i.e. $S=0$

So, the work done can be obtained as:

$⟹W=0$

Hence work done by friction force is zero.