A force F1 acts on a particle so as to accelerate it from rest to a velocity v. The force F1 is than replaced by F2

which decelerates it to rest.

(a) F1 must be equal to F2 (b) F1 may be equal to F2 (c) F1 must be unequal to F2 (d) None of these

Dear Jeet,

Even a very small force can accelerate an object at rest, but for smaller force the acceleration will be smaller. F₁ accelerates the body to velocity v, in some finite time which is not mentioned. Force is a vector quantity, and by convention F₁ is positive as it is along the direction of motion of the object.

The other force F₂ decelerates the object. Any finite force can decelerate a moving object. But this force opposes the direction of motion of the object so, it is negative.

Thus we conclude, the force F ₁ and F ₂ must be different. Even if they have same magnitude their direction will be opposite.

Correct answer is (c)

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