A block of mass 5 kg placed on a rough horizontal surface having coefficient of friction $\mu=0.4$.

Question

A block of mass 5 kg placed on a rough horizontal surface having coefficient of friction $\mu=0.4$. If a horizontal force of 40 N acts on it, then the acceleration of the block will be (Take $g = 10 \mathrm{~m/s}^2$)

Professor PC Thomas Classes · Answer

Limiting friction $f_k = \mu N = 0.4 	imes 5 	imes 10 = 20 \mathrm{~N}$. Applied force $P = 40 \mathrm{~N}$. Since $P > f_k$, the block moves. Net force $F_{net} = P - f_k = 40 - 20 = 20 \mathrm{~N}$. Acceleration $a = F_{net} / m = 20 / 5 = 4 \mathrm{~m/s}^2$.