A rectanglar body is held at rest by pressing it againts a vertical wall for which `mult1` . Which of the following is generally ture?

Options

A. It will be easier to hold the block if the surfaces in contact are smooth and polished
B. the required pressing force is smaller than the weight mg of the body
C. The required pressing force is greater than the weight mg of the body
D. The required pressing force is independent of friction between surfaces in contact

Answer

C

Explanation

The frictional force opposes the downward motion of the body due to its weight. Hence the surface should be rough and not smooth.
For equilibrium of the block P=R and `F_s=mg`
`:." "mu_s=(F_s)/R=(mg)/P" ":." "P=(mg)/(mu_s)`
as `mult1,Pgtmg`
`:.` The required pressing force is greater than the weight mg of the body.