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? | Learn NCERT solution | Education portal Class 11 Physics | Study online Unit-5 Laws Of Motion



Q.5:- 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:-



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 ms-2
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 = 6 s