Question

which statement explains why the coin fell straight down into the jar instead of remaining on the hoop?
a. the coin was at rest until the hoop was removed. once the hoop was gone, the unbalanced force of gravity caused the coin to fall.
b. moving the hoop applied an action force on the coin. since the hoop was gone, gravity applied a reaction force on the coin.
c. the hoop had less mass than the coin, so a smaller force of gravity acted on the hoop. the larger force of gravity on the coin made it fall.
d. the acceleration of the coin falling into the jar was equal and opposite to the acceleration of the hoop.

Explanation:

• Option A: According to Newton's first law (law of inertia), an object at rest stays at rest unless acted upon by an unbalanced force. The coin was at rest on the hoop. When the hoop was removed, the only significant force acting on the coin was gravity (an unbalanced force), which caused it to fall.
• Option B: Gravity is not a reaction force. Action - reaction forces act on different objects. When the hoop is moved, it's not about action - reaction in the way described here. The coin's fall is due to gravity as an unbalanced force, not a reaction force.
• Option C: The fact that the hoop has less mass than the coin is not the direct reason for the coin falling. The key is the unbalanced force (gravity) acting on the coin when the hoop (which was providing a normal force to balance gravity initially) is removed.
• Option D: There is no basis for the claim that the acceleration of the coin falling is related to the acceleration of the hoop in an "equal and opposite" way in the context of why the coin falls. The coin falls because of the unbalanced force of gravity acting on it after the hoop is removed.

Answer:

A. The coin was at rest until the hoop was removed. Once the hoop was gone, the unbalanced force of gravity caused the coin to fall.