Q20Long answer
An object starting from rest travels 20 m in first 2 s and 160 m in next 4 s. What will be the velocity after 7 s from the start.
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s1 = ut + at or 20=0+ a (2)2 or a= 10 m s–2, 2 2 v = u + at = 0 + (10 × 2) = 20 m s–1 1 1 s2 = 160 = vt′ + a′ (t′ )2 = (20 × 4) + ( a′ × 16) ⇒ a ′ =10 m s–2 2 2 Since acceleration is the same, we have v ′ =0+ (10 × 7) = 70 m s–1