Question

A solid sphere of mass $m$ is placed on rough inclined plane. The coefficient of friction $\mu$, is insufficient to start pure rolling. The sphere slides a length $l$ on the incline from rest and its kinetic energy becomes $K$. Then work done by friction will be :

• A. $-\mu mglcos\theta$
• B. $-mglsin\theta +K$
• C. $-\frac{2}{5}\mu mglsin\theta +K$
• D. None of these

Answer 1

The correct option is B $-mglsin\theta +K$

By Work Energy Theorem,

$W_{mg}+W_f=\Delta KE$

$mglsin\theta +W_f=K-0=K{W}_f=-mglsin\theta +K$