Question

streamer moves with velocity $3 \,km \,h^{-1}$ in and against the direction of river water whose velocity is $2\, km\, h^{-1}$. Calculate its total time for total journey if the boat travels 2 km in direction of the stream and then back to his place.

• A. 2 h
• B. 2.5 h
• C. 2.4 h
• D. 3 h

Answer 1

Answer: (C)

2.4 h

Answer 2

The velocity of streamer while moving down-stream $= 3 \,km \,h^{-1} + 2 \,km\, h^{-1}$ = $5\, km\, h^{-1}$ and while moving upstream $= 3 \,km\, h^{-1} - 2\, km\, h^{-1} = 1\, km\, h^{-1}$. Total time taken $\frac{2\, km}{5 \,km \,h^{-1}} + \frac{2\, km}{1 \,km\, h^{-1}} = 0.4 \,h + 2\, h = 2.4 \,h$