Question

A dog (mass 11.7 kg) sits on a sled (mass 5.1 kg) that is being pushed with a force of 35 N on a flat snowy surface. If the acceleration of both is 1.7 m/s2, what is the coefficient of kinetic friction for the sled sliding on the snow?

Answer 1

The Newton's second law states

$$ma=F-F_{\rm{fric}}$$

$$(11.7+5.1)1.7=35-F_{\rm{fric}}$$

So, the friction force

$$F_{\rm{fric}}=6.44\:\rm{N}$$

The coefficient of kinetic friction

$$\mu_k=\frac{F_{\rm{fric}}}{mg}=\frac{6.44}{(11.7+5.1)9.81}=0.04$$