Question

A constant retarding force of 50 N is applied to a body of mass 20 kg moving initially with a speed of 15 m s-1. How long does the body take to stop ?

Answer 1

Given: The mass of the body is 20 kg, the initial speed of the body is 15 m/s , the retarding force on the body is 50 N and the final velocity of the body is 0 m/s .

Newton’s second law of the motion is given as,

F=ma

By substituting the given values in the above expression, we get

−50 N=( 20 kg )a a=−2.5 m/ s 2

Apply the first equation of motion.

v=u+at

By substituting the given values in the above expression, we get

0=15 m/s +( −2.5 m/ s 2 )t t= 15 m/s 2.5 m/ s 2 =6 s

Thus, the body takes 6 s to stop.