Upstream: When the boat moves against the current of the river (i.e. in opposite direction), then the relative speed of the boat is the difference of the speed of the boat and stream. It is known as upstream speed.
Remember it with UP as going up the hill means against the direction of the force (speed) of the river.
If speed of boat or swimmer is x km/h and the speed of stream is y km/h then,
- Speed of boat upstream = (x − y) km/h
Downstream: When the boat moves with the current of the river (i.e. in same direction), then the relative speed of the boat is the sum of the speed of the boat and stream. It is known as downstream speed.
Remember it with DOWN as going down the hill means towards the direction of the force (speed) of the river.
If speed of boat or swimmer is x km/h and the speed of stream is y km/h then,
- Speed of boat downstream = (x + y) km/h
Important Points
- When speed of boat is given then it means speed in the still water, unless it is stated otherwise.
Some Basic Formulas
- Speed of boat in still water is
= ½ (Downstream Speed + Upstream Speed)
- Speed of stream is
= ½ (Downstream Speed – Upstream Speed)
No comments:
Post a Comment