The speed of boat is 5 km/hr in still water. It crosses a river of width of 1 km along a shortest possible path in 15 minutes. Then velocity of the river is:

Question

The speed of boat is 5 km/hr in still water. It crosses a river of width of 1 km along a shortest possible path in 15 minutes. Then velocity of the river is: (A) 1 km/hr (B) 2 km/hr (C) 3 km/hr (D) 4 km/hr

Tardigrade Admin · Accepted Answer

Here: speed of boat in still water upsilon b =5 km/hr width of river = 1 km Time taken to cross the river along shortest possible path = 15 min = (1/4) hour Hence resultant velocity of the boat =4 km text/hr Then the velocity of river =√(5)2-(4)2=3 km text/hr

Q. The speed of boat is 5 km/hr in still water. It crosses a river of width of 1 km along a shortest possible path in 15 minutes. Then velocity of the river is:

1 km/hr

2 km/hr

3 km/hr

4 km/hr

Here: speed of boat in still water $υ_{b} = 5 km / h r$ width of river = 1 km Time taken to cross the river along shortest possible path = 15 min = $\frac{1}{4}$ hour Hence resultant velocity of the boat $= 4 km / h r$ Then the velocity of river $= (5)^{2} - (4)^{2} = 3 km / h r$

Q. The speed of boat is 5 km/hr in still water. It crosses a river of width of 1 km along a shortest possible path in 15 minutes. Then velocity of the river is:

1 km/hr

2 km/hr

3 km/hr

4 km/hr

Here: speed of boat in still water υb​=5km/hr width of river = 1 km Time taken to cross the river along shortest possible path = 15 min = 41​ hour Hence resultant velocity of the boat =4km/hr Then the velocity of river =(5)2−(4)2​=3km/hr

Here: speed of boat in still water $υ_{b} = 5 km / h r$ width of river = 1 km Time taken to cross the river along shortest possible path = 15 min = $\frac{1}{4}$ hour Hence resultant velocity of the boat $= 4 km / h r$ Then the velocity of river $= (5)^{2} - (4)^{2} = 3 km / h r$