Bill and his daughter Susan are both standing on identical skateboards (with really good frictionless ball bearings),initially at rest.Bill weighs three times as much as Susan.Bill pushes horizontally on Susan's back,causing Susan to start moving away from Bill.Just after Bill stops pushing,
A)Susan and Bill are moving away from each other,and Susan's speed is three times that of Bill.
B)Susan is moving away from Bill,and Bill is stationary.
C)Susan and Bill are moving away from each other,with equal speeds.
D)Susan and Bill are moving away from each other,and Susan's speed is one-third that of Bill.

Question

Quizplus · Accepted Answer

According to Newton's third law of motion, when Bill pushes Susan, Susan pushes back on Bill with an equal and opposite force. This results in both of them moving away from each other. However, because Bill is three times as heavy as Susan, his acceleration will be one-third of Susan's, according to the formula $F = ma$. Therefore, Susan will move away at a speed three times that of Bill, making option A correct.

Bill and His Daughter Susan Are Both Standing on Identical