Two particles A and B move only due to their mutual interaction. At any time t, $\overrightarrow{a}_{A}$ and $\overrightarrow{a}_{B}$ are their accelerations; $\overrightarrow{v}_{A}$ and $\overrightarrow{v}_{B}$ their velocities; $W_{A}$ and $W_{B}$ the work done by the mutual force; $m_{A}$ and $m_{B}$ their masses. Which is always correct?
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Question

Two particles A and B move only due to their mutual interaction. At any time t, $\overrightarrow{a}_{A}$ and $\overrightarrow{a}_{B}$ are their accelerations; $\overrightarrow{v}_{A}$ and $\overrightarrow{v}_{B}$ their velocities; $W_{A}$ and $W_{B}$ the work done by the mutual force; $m_{A}$ and $m_{B}$ their masses. Which is always correct?

Options

G1 Physics · Accepted Answer

Only internal forces act, so total linear momentum remains constant. Since the system starts with the stated momenta, the always-valid relation is mₐvₐ + mᵦvᵦ = constant; for the keyed condition it is zero. Correct answer: B.