A block of mass 5kg is resting on a rough surface as shown in the figure. It is acted upon by a force of F towards right. Find frictional force acting on block when 25N.

Explanation

Maximum value of frictional force that the surface can offer is
`f_("max") = f_("lim") = mu_(s) N `
`= 0.6 xx 5 xx 10 = 30 ` newton

Therefore, it `F le f_("max")` body will be at rest and f = F or `F gt f_("max")` body will more and `f= f_(k)`
`F = 25 N lt F_("max")` `:. f_(s) = 25 N `