Question

A small block of mass '$m$' is kept on a rough inclined surface of inclination $\theta$ fixed in a lift . The lift moves up with a uniform velocity $v$ and the block does not slide on the incline . The work done by the force of friction on the block in time $t$ will be:

• A. zero
• B. $mgvtco{s}^2\theta$
• C. $mgvtsi{n}^2\theta$
• D. $mgvtsin2\theta$
  

Answer 1

The correct option is C $mgvtsi{n}^2\theta$

As there is inclination of $\theta$, so friction will balance the $mgsin\theta$
therefore,
$f=mgsin\theta$
then, vertical displacement in time $t=vt$

work done = $fvtsin\theta$
= $mgvtsi{n}^2\theta$