Answer
a. Force needed to keep the pucks moving, greatest to least: A = B = C
b. Force needed to stop the pucks in the same time interval, greatest to least: C, B, A.
Work Step by Step
a. According to Newton's first law, the pucks will tend to remain in motion at constant velocity if there is no net force. Therefore, the net force on each is zero.
b. Puck C is moving faster than identical puck B, which is moving faster than identical puck A.
To stop each of them, puck C will undergo the greatest change in velocity and hence the greatest acceleration, followed by puck B, then last of all, puck A.
According to Newton's second law, for identical masses, a larger net force is required to produce a larger acceleration.
