Q31 of 124 Page 74

How long will it take a force of 10 N to stop a mass of 2.5 kg which is moving at 20 m/s?

Force applied (F) = -10 N (since the force is acting in the opposite direction of motion or opposing the motion)

Mass of body (m) = 2.5kg


Initial velocity of body (u) = 20m/s


Final velocity of body (v) = 0m/s


According to Newton's second law of motion


F = ma


-10 = 2.5×a


-10/2.5 = v-u/t (since a = v-u/t)


-4t = 0 - 20


t = -20/-4


t = 5 sec


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For how long should a force of 100 N act on a body of 20 kg so that it acquired a velocity of 100 m/s?

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The velocity of a body of mass 10 kg increases from 4 m/s to 8 m/s when a force acts on it for 2 s.

(a) What is the momentum before the forces acts?


(b) What is the momentum after the force acts?


(c) What is the gain in momentum per second?


(d) What is the value of the force?

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(i) The velocity with which the gun recoils.


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