Question

a motor launch 30 s to travel 120 m upstream and 20 s to travel the same distance downstream.calculate speed of current and launch
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Answer 1

Answer:

Speed of boat in upstream = 15 km/hr

Distance = 1.5 km

Time = t

1

=

15

1.5

= 6 min

Distance move by float in this time

5×

10

1

=

2

1

km

Speed of boat w.r.t. float,

20km/hr,t

2

=

20

2 km

= 6 min.

Answer 2

Answer:

The speed of the current is 1 m/s and the speed of the launch be 5m/s

Explanation:

Let the speed of the motor launch in still water be u m/s and the speed of current be v m/s

Let the total distance be 120 m.

In case of downstream,

$\frac{120}{u-v}= 30$ => $u - v = 4$

In case of upstream,

$\frac{120}{u+v}= 20 => u+v = 6$

Solving,

we get u = 5m/s and v = 1m/s

The speed of the current is 1 m/s and the speed of the launch be 5m/s