Question

hello
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please help me solve this question answer not on google. ​

Answer 1

Explanation:

He needs to cross exactly at the opposite point to the point of his start. The river is flowing perpendicularly to him. The river is flowing at 3m/s and he needs to swim at 5m/s making an angle with the starting point so that he actually reaches the opposite point. This angle is arc sin (3/5) or sine inverse of (3/5) i.e. 36.9° angle.

This is a 3-4-5 right angled triangle problem if you visualize. The man swims actually at speed 5m/s at an angle 36.9° to the point of start but due to wave speed of 3m/s he reaches exactly along the perpendicular (i.e. the width of the river) to the opposite point of his start. If you go a little deeper, The man actually travels 125 meter making an angle of 36.9° but due to river waves his movement made him move sidewise by 75 meters so that he can reach exactly the opposite point which is 100 meter away (the width of the river). 75-100-125 i.e. 3-4-5 right angle.

And, yeah, since he will have to swim 125 meters actually but due to wave speed ot would seem like 100 meters, time required to cross the river (125m)/(5m/s)= 25 seconds.

Hope this helps.