During a demonstration of Newton's laws of motion, a student used the setup shown in Figure 1. The student flicked the index card with a fingertip, and the coin fell straight down into a plastic cup as
shown in Figure 2.
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Figure 1
Figure 2
Which of these best explains why the coin feil straight down into the cup instead of remaining on the
index card?
F. The coin was at rest until the card was removed, so it tended to remain in the same location.
Once the card was gone, the unbalanced force of gravity caused the coin to fall.
6. Moving the card applied an action force on the coin. Since the card was gone, gravity applied a
reaction force on the coin.
H. The card had less mass than the coin, so a smaller force of gravity acted on the card. The
larger force of gravity on the coin made it fall.
J. The acceleration of the coin falling into the cup was equal and opposite to the acceleration of
the card.