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A body begins moving from rest under a steady force. If the displacement in the first 10 s is S1 and the displacement in the first 20 s is S2, then which relation is true?

1. S2 = 3S1
2. S2 = 4S1
3. S2 = S1
4. S2 = 2S1

Correct answer: S2 = 4S1

Solution

Starting from rest with constant acceleration, displacement S = (1/2)a t^2, so S is proportional to t^2. Hence S2/S1 = (20/10)^2 = 4, giving S2 = 4 S1.

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