Question

Determine the friction force for following cases
a) P = 100 N
b) P = 0 N

And the force P required to start the motion up the incline from rest

Answer 1

The friction force

$F_f=\mu N=\mu mg\cos\alpha$

Assume that $\mu=0.3$ and $P$ is the weight of the body. We get

a) $F_f=\mu N=0.3\cdot100=30(N)$

b) $F_f=\mu N=0.3\cdot0=0$

The force P required to start the motion up the incline from rest

$P>mg\sin\alpha+F_f$