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Aptitude Topics

Relative Speed

Relative speed measures the rate at which the distance closes or expands between two moving objects. It allows you to freeze one object in place while transferring all motion to the other frame.

Fundamental Principles

Opposite Direction Architecture

When two objects move toward each other (or away from each other in opposite directions), their relative speed is the sum of their individual speeds: $S_{rel} = S_1 + S_2$.

Same Direction Architecture

When two objects move in the same direction (e.g., a chase scenario), their relative speed is the difference between their individual speeds: $S_{rel} = |S_1 - S_2|$.

Essential Formulation Tips

  • Relative speed calculations are only valid when both objects are moving during the exact same time frame. If start times differ, calculate the initial displacement first.
  • In chase problems, the time required to catch up is always equal to the initial separation distance divided by the relative speed difference.

Shortcut Execution Techniques

  • To simplify complex chase scenarios, imagine the leading target is perfectly stationary and evaluate the closing gap using only the net speed difference.

Contextual Inquiries (FAQs)

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