Question

An object has a mass of 60 kg. It decelerates from 50 m/s to 20 m/s when a resultant force of 300 N acts on it. For how long does the force act?
A 0.071 s
B 0.17 s
C 6.0 s
D 14 s​

Answer 1

• Force=300N
• Mass=60kg

Find Acceleration

$\\ \rm\longmapsto F=ma$

$\\ \rm\longmapsto a=\dfrac{F}{m}$

$\\ \rm\longmapsto a=\dfrac{-300}{60}$

$\\ \rm\longmapsto a=-5m/s^2$

Now

• u=50m/s
• v=20m/s

Using 1st equation of kinematics

$\\ \rm\longmapsto v=u+at$

$\\ \rm\longmapsto t=\dfrac{v-u}{a}$

$\\ \rm\longmapsto t=\dfrac{20-50}{-5}$

$\\ \rm\longmapsto t=\dfrac{-30}{-5}$

$\\ \rm\longmapsto t=6$