Question

1. A 30-kg sled is pulled by a rope at ​constant speed.​ ​The tension in the rope is 50 N.

a. Draw a quantitatively accurate force diagram

b. Calculate the coefficient of friction (μ) between the floor and the sled.

2. Calculate the acceleration of the sled from problem 1, if the coefficient of friction was 0.

Answer 1

(a) The free body diagram

(b) The Newton's first law says

$$F_{\rm fric}=T=50\:\rm N.$$

Hence, the coefficient of kinetic friction between the floor and the sled

$$\mu=\frac{F_{\rm fric}}{mg}=\frac{50}{9.8\times 30}=0.17.$$

(c) The Newton's second law says

$$a=\frac{F_{\rm net}}{m}=\frac{T}{m}=\frac{50}{30}=1.7\rm m/s^2.$$