Question

A force of 70 N is applied to a 28 kg rock causing it to slow down from 25 m/s to 15 m/s, a change in velocity of 10 m/s. How long was that force applied?

Answer 1

Answer: 4 s

Explanation:

Given

The applied force is 70 N

mass of the rock is 28 kg

initial velocity $u=25\ m/s$

final velocity $v=15\ m/s$

Deceleration provided by force is

$a=-\dfrac{70}{28}=-2.5\ m/s^2$

using the equation of motion

$v=u+at\\\Rightarrow 15=25-2.5t\\\Rightarrow 2.5t=10\\\Rightarrow t=4\ s$