Question

a 50 kg sled is pulled along a level surface at constant velocity by a constant force of 200n at an angle of 30° what is the coefficient of friction between the sled and the surface

Answer 1

Given:

$F=200\:\rm N$

$m=50\:\rm kg$

$\theta=30^\circ$

The Newton's second law gives

$$F_x=F\cos\theta-F_f=ma_x=0$$

$$F_y=N+F\sin\theta-mg=ma_y=0$$

Also we must use the definition of friction force

$$F_f=\mu N$$

These three equations give

$$\mu=\frac{F\cos \theta}{mg-F\sin\theta}$$

$$\mu=\frac{20\cos 30^\circ}{50*9.8-200\sin 30^\circ}=0.044$$