Question

A force $f_1$ acts on a particle, so as to accelerate it from rest to a velocity v. If the force $f_1$ is replacedby $f_2$, which decelerates it to rest, then_____

• A. $f_1$ may be equal to $f_2$
• B. $f_1$ must not to be equal to $f_2$
• C. $f_1$ and $f_2$ must be zero
• D. $f_1$ must be equal to $f_2$

Answer 1

Answer: (A)

$f_1$ may be equal to $f_2$

To decelerate a body, a force must be applied opposite to the direction of velocity, irrespective of its magnitude.

According to condition of motion under two forces, $f_1$ and $f_2$ must be acting in opposite directions and may be equal, not necessarily must be equal.