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Q5.5 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?

Answers (1)


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\ =\ \frac{50}{20}\ =\ - 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\ =\ \frac{15}{2.5}\ =\ 6\ s

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

Posted by

Devendra Khairwa

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