Question

An object of mass m held against a
vertical wall by applying horizontal
force F as shown in the fi gure. Th e
minimum value of the force F is

Answer 1

The gravitational force acting on the block will attract it downwards.


To cancel the motion in downward, An equal force should be applied in the upward direction.



The upward force will be frictional force between the contact surfaces of wall and the block.

So , if static frictional constant is u,
the minimum force F will create a frictional force or the normal force on the block.

So the frictional force=u×Normal force
f=uF

This frictional force should be equal to the gravitational force to get the resultant force zero.

So ....

uF=mg
or..
F=mg/u