Q. A rough vertical board has an acceleration $'a'$ so that a $2\ kg$ block pressing against it does not fall. The coefficient of friction between the block and the board should be
A) $> g/a$
B) $< g/a$
C) $= g/a$
D) $> a/g$
Explanation
(a) For the limiting condition upward friction force between board and block will balance the weight of the block
$i.e$.$F > mg$
$\Rightarrow \mu(R) > mg$
$\Rightarrow \mu(ma) > mg$
$\Rightarrow \mu > \frac{g}{a}$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.