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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?

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We are given the retarding force. So we can find the deacceleration this force is causing.

By Newton's second law of motion, we get :

                                                 F = ma

or                                         -50 = (20)a

or                                               a = frac5020 = - 2.5 m/s^2

Now we will use the first equation of motion, 

                                                 v = u + at

The final velocity, in this case, will be zero (Since the vehicle stops).

                                               0 = 15 + (-2.5)t

Thus                                        t = frac152.5 = 6 s

Thus the time taken to stop the vehicle is 6 sec.

Posted by

Deependra Verma

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