Particle A is projected horizontally from (0,80) m at 20 m/s. Simultaneously B is projected horizontally from (60,20) m at 10 m/s in the same direction. Take g=10 m/s². Before either hits the ground, their minimum separation is:
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Question

Particle A is projected horizontally from (0,80) m at 20 m/s. Simultaneously B is projected horizontally from (60,20) m at 10 m/s in the same direction. Take g=10 m/s². Before either hits the ground, their minimum separation is:

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G1 Physics · Accepted Answer

Common gravity cancels in relative motion: r⃗_BA=(60−10t)î−60ĵ. B hits ground at t=2 s, before the unrestricted closest time 6 s. Thus the physical minimum is at t=2 s: d=√(40²+60²)=20√13 m.