A river 4.0 miles wide is flowing at the rate of (2 miles / hr ). The minimum time taken by a boat to cross the river with a speed v=4 miles / hr (in still water) is approximately

Question

A river 4.0 miles wide is flowing at the rate of (2 miles / hr ). The minimum time taken by a boat to cross the river with a speed v=4 miles / hr (in still water) is approximately (A) 1 hr and 0 minute (B) 2 hr and 7 minutes (C) 1 hr and 12 minutes (D) 2 hr and 25 minutes

Tardigrade Admin · Accepted Answer

Minimum time is taken when the boat crosses the river at right angles to its flow. The resultant velocity of boat and river should be at right angles to flow of river. t min =(D/v)=(4/4)=1 hr

Q. A river $4.0$ miles wide is flowing at the rate of (2 miles $/ h r$ ). The minimum time taken by a boat to cross the river with a speed $v = 4$ miles $/ h r$ (in still water) is approximately

1 hr and 0 minute

2 hr and 7 minutes

1 hr and 12 minutes

2 hr and 25 minutes

Minimum time is taken when the boat crosses the river at right angles to its flow. The resultant velocity of boat and river should be at right angles to flow of river.
$t_{m i n} = \frac{D}{v} = \frac{4}{4} = 1 h r$

Q. A river 4.0 miles wide is flowing at the rate of (2 miles /hr ). The minimum time taken by a boat to cross the river with a speed v=4 miles /hr (in still water) is approximately