Two identical balls are projected vertically upward from the same point at an interval of 2 s with the same initial speed 40 m s⁻¹. Take g=10 m s⁻². Height at which they collide is:
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Question

Two identical balls are projected vertically upward from the same point at an interval of 2 s with the same initial speed 40 m s⁻¹. Take g=10 m s⁻². Height at which they collide is:

G1 Physics · Accepted Answer

Let t be time after first launch. Equating heights: 40t-5t² =40(t-2)-5(t-2)². This gives t=5 s. Height=40(5)-5(25)=75 m. Option B.