question_answer 70)

                  A block of mass M is held against a rough vertical wall by pressing it with a finger. If the coefficient of friction between the block and the wall is \[\mu \] and the acceleration due to gravity is g, calculate the minimum force required to be applied by the finger to hold the block against the wall?

Answer:

                  Let F be the minimum force required to be applied by the finger to hold the block against the wall.                 Normal reaction of the wall on the block, \[R=F\]                 If f is the force of friction, the \[f=\mu R=\mu F\]                 For the block not to fall, \[f=Mg\]             or \[\mu F=Mg\] or \[F=\frac{Mg}{\mu }\]