A river flows at 9 km/h. A boat moves downstream with speed 27 km/h relative to water. A person in the boat throws a ball vertically upward at 10 m/s. Find the horizontal range of the ball as seen by an observer on the bank. Take g=10 m/s².
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Question

A river flows at 9 km/h. A boat moves downstream with speed 27 km/h relative to water. A person in the boat throws a ball vertically upward at 10 m/s. Find the horizontal range of the ball as seen by an observer on the bank. Take g=10 m/s².

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G1 Physics · Accepted Answer

Ground speed of the boat is 9+27=36 km/h=10 m/s. The ball retains this horizontal speed. Time of flight for vertical throw is T=2u/g=2 s. Hence range=10×2=20 m.