Question

A small block of mass m is kept on 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 will be

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

Answer 1

Answer: (C)

$mgvt{\sin }^2\theta$

$W_f=f\sin \theta S$
$=\left(mg\sin \theta \right)\left(\sin \theta \right)\left(vt\right)$
$=mg{\sin }^2\theta vt$