upstream 4km in 2 hours.
Find her speed of rowing in still water and the speed of the current.
Soln.
Let Ritu’s speed in still water be x km/hr and the speed of current be y km/hr
Speed of the Boat in upstream = (x – y ) km / hr
Speed of the boat in downstream = (x + y) km / hr
Distance covered in downstream = 20 km
Time taken in down stream = 2 hrs
We Know that,
Speed = Distance
Time
x + y = 20
2
x + y = 10 ….(i)
Upstream
Downstream
What we need to find?
In this question we come across two new terms
Upstream and Downstream
The boat and the stream travel in
opposite direction,
we say boat is moving upstream
So in upstream the speed will increase or decrease??
Speed increases
Distance travelled in upstream is
Distance travelled in downstream is
Similarly in upstream the speed of the boat Decreases
Speed Reduces
5 – 2 = 3 km/hr
What will happen to your speed?
And somebody opposes you with the speed of 2km / hr
Suppose you are moving with speed of 5 km/hr.
Eg : Sea, River etc
Stream means moving water or running water from higher level to lower level
Eg : Swimming pool, pond etc
Still water means the water which is not moving
The boat and the stream travel in same direction,
We say boat is moving Downstream
∴
∴
Distance covered in upstream = 4 km
Time Taken in upstream = 2 hrs
We Know that,
Speed = Distance
Time
x - y = 4
2
∴
∴
x - y = 2 ….(ii)
Solve the equations with either substitution or elimination method
x
= 6
Substituting x = 6 in (i)
y = 4