The speed of a boat in still water is 5 km/hr and the speed of current is 3 km/hr. If the time taken to reach a certain distance downstream is 4 hours, the time it will take to go to same distance upstream is
The speed of a boat in still water is 5 km/hr and the speed of current is 3 km/hr. If the time taken to reach a certain distance downstream is 4 hours, the time it will take to go to same distance upstream is
1). 1 hr
2). 4 hrs
3). 16 hrs
4). 2 hrs
1 answers
As per the basic formula of speed,
S = D/T
Where S = Speed
D = Distance
T = Time
Now when the boat goes downstream the boat is flowing along with the water hence speed of the boat will be increased by the speed of the current
Downstream Speed = Speed of boat in still water + Speed of stream
Downstream Speed = 5 + 3
Downstream Speed = 8 km/hr
Now as the time taken to cover the distance downstream is 4 hours
⇒ 8 = D/4
⇒ D = 32 Kms
Now when the boat goes upstream the boat is flowing against the flow of water hence the relative speed of the boat will be decreased by the speed of current
Upstream speed = Speed of boat in still water-Speed of stream
Upstream speed = 5 - 3
Upstream speed = 2 km/hr
∴ Time taken to cover the distance upstream = D/S = 32/2 = 16 hours
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