A block P is placed on a larger block Q, which is initially at rest on a smooth horizontal surface. Block Q is suddenly pulled horizontally, causing P to slip backward relative to Q. Which of the following statements best explains this observation?
Block P tends to remain at rest due to inertia while block Q moves forward.
Newton's first law states that a body continues in its state of rest or uniform motion unless an external force acts on it. This tendency to resist a change in the state of rest is called inertia of rest, and it depends only on the mass of the body.
When Q is pulled suddenly, it accelerates forward at once. The only horizontal force on P is friction from Q, which is too small to give P the same sudden acceleration, so P tends to stay where it was in the ground frame.
Since Q moves forward underneath it while P lags behind, P appears to slip backward relative to Q. This is the same effect as a passenger jerking backward when a bus starts suddenly, or a coin staying on the glass when the card is flicked away.
No backward push acts on P; inertia does not increase with the acceleration of another body, as it is fixed by P's own mass; and gravity acts vertically downward, so it cannot cause any horizontal sliding.
Hence, Block P tends to remain at rest due to inertia while block Q moves forward.
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