A ball is projected vertically upward from the ground with speed 30 m s⁻¹. Two seconds later, another ball is projected upward from the same point with the same speed. Taking g=10 m s⁻², they meet:
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Question

A ball is projected vertically upward from the ground with speed 30 m s⁻¹. Two seconds later, another ball is projected upward from the same point with the same speed. Taking g=10 m s⁻², they meet:

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G1 Physics · Accepted Answer

Let t be time measured from the first projection. For the first ball: y₁ = 30t − 5t². For the second ball, for t≥2: y₂ = 30(t−2) − 5(t−2)². Equating y₁=y₂ gives t=4 s. Then y = 30(4) − 5(16) = 40 m.