Question

H. A swimmer swims 300 m in still water and then returns following the same path. He takes a total
of 12 minutes to come back to his initial position. Find his speed in:
(a) ms
(b) km h-!​

Answer 1

Answer:

Correct option is

D

48.125 mins

Speed of the boat when it travels upstream =7−3=4m/sec

Speed of the boat when it travels downstream =7+3=10m/sec

Now,

As soon as the float falls, it will travel downstream at the speed of 3m/sec

And in the meantime, the boat has also traveled upstream a distance of 4.2 km

So,

Time spend on traveling upstream by boat =

4

4200

=1050sec

In the meantime, the float would had traveled downstream by =1050×3 = 3150 m

Hence, the total distance between the float and the boat will be =3150 + 4200 = 7350 m

Now, the relative speed between a boat and the float =10-3=4 m/sec

Hence time taken = 7350/4=1837.5 sec

Hence, total time spent = 1837.5+1050=2887.5 sec

This is 2887.5 /60= 48.125 mins

Hence the float and the boat will meet in 48.125mins

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