Consider a perfectly horizontal air hockey table. A puck that is floating freely

Question

Consider a perfectly horizontal air hockey table. A puck that is floating freely on the table has no net force on it. The upward force by the air on the puck is equal in strength but opposite in direction to the gravitational force by the Earth on the puck. These two forces, therefore, cancel out.

Place the puck at rest, floating on the table as described above. Now tap it on its left hand side with your finger. Which one of the following statements would be true? (note: after the tap means after the finger is no longer touching it)

The puck undergoes an acceleration to the right and its speed increases in that direction only for the duration of the tap, after that it slows down.

The puck undergoes an acceleration to the right and its speed increases in that direction only for the duration of the tap, after that it goes at a constant speed.

none of these answers is correct

The puck undergoes an acceleration to the right; its speed continually increases starting with the tap and continuing after the tap.

Explanation / Answer

In this case, there is a net resultant force on the puck by your finger only for the duration of the flick. This force causes an acceleration of the puck only for the duration of the flick, after which the puck moves off to the right with a constant velocity.

Therefore, the correct answer:

The puck undergoes an acceleration to the right and its speed increases in that direction only for the duration of the tap, after that it goes at a constant speed.

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