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A body moves with constant acceleration. It covers 65 m during the 5th second and 105 m during the 9th second. What distance will it cover in 20 s?

1. 2040 m
2. 240 m
3. 2400 m
4. 2004 m

Correct answer: 2400 m

Solution

Distance in nth second = u + a(n-1/2): u+4.5a=65 and u+8.5a=105 give a=10, u=20. In 20 s, s = 20*20 + (1/2)(10)(20^2) = 400 + 2000 = 2400 m.

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