Question

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

Answer 1

Retarding force, F = –50 N

Mass of the body, m = 20 kg

Initial velocity of the body, u = 15 m/s

Final velocity of the body, v = 0

Using Newton’s second law of motion, the acceleration (a) produced in the body can be calculated as:

F = ma 

–50 = 20 × a

a = -50/20 = -2.5 m/s² 

Using the first equation of motion, the time (t) taken by the body to come to rest can be calculated as:

v = u + at

t = -u/a = -15/-2.5 = 6s