A firecracker exploding on the surface of a lake is heard as two sounds a time interval t apart by a man on a boat close to water surface. Sound travels with a speed u in water and a speed v in air. The distance from the exploding firecracker to the boat is
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Question

A firecracker exploding on the surface of a lake is heard as two sounds a time interval t apart by a man on a boat close to water surface. Sound travels with a speed u in water and a speed v in air. The distance from the exploding firecracker to the boat is

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G1 Physics · Accepted Answer

Step 1: If distance is d, arrival-time difference is t = d/v − d/u = d(u−v)/(uv), with u>v. Step 2: Therefore d = uvt/(u−v). Final: D.