question_answer

A boy of mass m is sliding down a vertical pole by pressing it with a horizontal force F. If \[\mu \]is the coefficient of friction between his palms and the pole, the acceleration with which he slides down is

A) \[g\]                              

B) \[\frac{\mu F}{m}\]

C) \[g+\frac{\mu F}{m}\]               

D) \[g-\frac{\mu F}{m}\]

Correct Answer: D

Solution :

Here, normal contact force \[N=F\] and friction force, \[f=\mu N\]

So the free body diagram of boy is as shown adjacent in the above figure.

Now, \[ma=mg-f\]

\[\Rightarrow \]   \[a=g-\frac{\mu F}{m}\]