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Grade: upto college level


A swimmer wishes to cross a 500 m wide river flowing at 5 km/h. His speed with respect to water is 3 km/h. (a) If he heads in a direction making an angle θ with the flow, find the time he takes to cross the river. (b) Find the shortest possible time to cross the river.

6 years ago

Answers : (3)

Navjyot Kalra
askIITians Faculty
654 Points
							Sol. a) The vertical component 3 sin θ takes him to opposite side.
Distance = 0.5 km, velocity = 3 sin θ km/h
Time = Distance/(Velocity ) = 0.5/(3 sin⁡θ ) hr
= 10/sin θ min.
b) Here vertical component of velocity i.e. 3 km/hr takes him to opposite side.
Time = Distance/Velocity = 0.5/3 = 0.16 hr
∴ 0.16 hr = 60 x 16 = 9.6 =  10 minute.

6 years ago
rohan duseja
15 Points
the swimmer wont be able to make it only as the speed of river is more as compare to the swimmer 
he will drown for sure
one year ago
ankit singh
480 Points



Vertical componenet to opposite side =3KM/hr
one month ago
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