A boat moves with a speed of 5 km/h relative to water in a river flowing with a speed of 3 km/h and having a width of 1 km . The time taken around a round trip is

Question

A boat moves with a speed of 5 km/h relative to water in a river flowing with a speed of 3 km/h and having a width of 1 km . The time taken around a round trip is (A) 5 min (B) 60 min (C) 20 min (D) 30 min

Tardigrade Admin · Accepted Answer

Time taken by the boat to reach the other side is
Time

= \frac{distance}{relative speed}

Relative speed

10 mm = 5^{2} - 3^{2} - 16 = 4 km h^{- 1}

T = \frac{1 km}{4 km h ^{- 1}} = 0.25 h

To come back boat takes the same time, hence total time is

T^{'} = 2 \times 0.25 = 0.5 h

Also,

1 h = 60 min

∴ 30 mm 0.5 h = 30 min

Q. A boat moves with a speed of 5km/h relative to water in a river flowing with a speed of 3km/h and having a width of 1km . The time taken around a round trip is

5 min

60 min

20 min

30 min

Time taken by the boat to reach the other side is Time = relative speed distance ​ Relative speed 10mm=52−32​−16​=4kmh−1 T=4kmh−11km​=0.25h To come back boat takes the same time, hence total time is T′=2×0.25=0.5h Also, 1h=60min ∴30mm0.5h=30min

Q. A boat moves with a speed of $5 km / h$ relative to water in a river flowing with a speed of $3 km / h$ and having a width of $1 km$ . The time taken around a round trip is