Question

A 20 kg box is initially sliding across the floor at 10 m/s. If the force of friction on the box is 50 N, how far will the box slide before coming to a stop?

Answer 1

Question 18981

According to $2^{\mathrm{nd}}$ Newton's law: $ma = -F_f$, where $F_f$ is the friction force. So,

$a = -\frac{5}{2} m / s^2$. Also, $v = v_0 - at$, so at the moment of stop $t = \frac{v_0}{a} = 4s$. Hence, the box will slide $S = v_0 t - \frac{a t^2}{2} = 40 - 20 = 20m$ far.