Question

A boy swims 90m long pool. He covers the distance of 180m by swimming from one end to other end back along the same path. If he covers the first 90m at speed of 2m/s, then how fast he swim so that his average speed is 3m/s?

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Answer 1

Answer:

Your answer is given in the following steps-::

Length of the pool = 90m

Speed to cover first 90 m = 2 m/s

 Since,

Speed = distance / time or Time = distance / speed

Time taken to cover first 90 m = 90 / 2 = 45 sec

Time taken to travel the next 90 m back = t₂

Total distance = 180 m

Therefore,

Total time to cover 180 m = 45 + t₂

Average speed to travel 180 m = 3 m/s

or Average speed = Total distance covered / Total time taken or 3 m/s = 180 / 45 + t₂

By cross multiplication, we get the following result 3* (45 +t₂) = 180 or t2= 15

Hence , time taken to travel back 90 m = 15 sec

To cover his average speed is 3m/s ?

Speed = distance / time = 90 / 15 = 6 m/ s

Hence , he must swim with a speed of 6 sec to make his average speed to be 3 m/s

Answer 2

Given that, a boy swims 90m long pool. He covers the distance of 180m by swimming from one end to other end back along the same path.

Total distance covered by the boy is 180 m.

Also, the boy covers the first 90m at speed of 2m/s.

Distance = 90 m and speed = 2 m/s

We know that,

Time = Distance/Speed

t1 = 90/2 = 45 hr

Now,

Assume that the time taken to complete the next half distance is t2.

Time taken to cover 180 m = t1 + t2 = 45 + t2

Given that, the boy swims with an average speed of 3 m/s.

Average speed is defined as the ratio of total distance covered with respect to total time taken i.e.

Average speed = (Total distance covered)/(Total time taken)

→ 3 = 180/(45 + t2)

→ 1 = 60/(45 + t2)

→ 45 + t2 = 60

→ t2 = 15

Therefore, the time taken to complete the next half distance is 15 sec.

As per given condition we have to find the speed of the boy.

Speed = Distance/Time

From above calculations we have time is 15 sec and distance is 90 m (in second half).

Speed = 90/15 = 6

Therefore, the speed of the boy is 6 m/s.