A man can swim in still water with a velocity of 2.5km/h. He wants to cross the river flowing at a speed of 1.5km/h. He always swims at an angle of 120° with downstream. The width of river is 800m . Then the time in which he will cross the river is
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Answer:
0.37 hr = 22.2 Mins
Explanation:
A man can swim in still water with a velocity of 2.5km/h. He wants to cross the river flowing at a speed of 1.5km/h. He always swims at an angle of 120° with downstream. The width of river is 800m . Then the time in which he will cross the river is
River Speed = 1.5 km/hr
Man speed in still water = 2.5 km/hr and angle = 120°
Speed across Downstream = 2.5Cos120° = 2.5(-1/2) = -1.25 km
Speed toward other bank = 2.5Sin120° = 2.5(√3/2) = 1.25√3
Net Speed = (1.5 - 1.25) i + 1.25√3 j
= 0.25i + 1.25√3 j
only 1.25√3 speed will help him to cross river width
=> 1.25√3 * time = 0.8 800 m = 0.8 km
=> Time = 0.64/√3
=> Time = 0.37 hr = 22.2 Mins
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