Question

dolphin swims from one end to anether
in a swimming pool with a length
50 m at a speed of 20 km/h and
returns with a speed of 30 km/h
Find the aug. swimming speed (in km/h)​

Answer 1

AnswEr :

Given that length of swimming pool is 50 m.

Dolphin goes to other end with speed of 20 km/h. And returns with a speed of 30 km/h.

We have to find average speed of dolphin.

From the data :

Distance b/w two points (d) = 50 m = 50/1000 km = 0.05 km

Speed of 1st step (s1) = 20 km/h

Speed of 2nd step (s2) = 30 km/h

We know the formula :-

Distance = Speed × Time

⇒ 0.05 = 20 × Time

⇒ Time = 0.05/20

⇒ Time1 = 1/400 h

Time in 2nd step :

⇒ Time = 0.05/30

⇒ Time2 = 1/600 h

Now we know that,

Average speed = Total distance/Total time

⇒ Av. speed = (0.05 + 0.05)/(1/400 + 1/600)

⇒ Av. speed = 0.1/[ (3 + 2)/1200 ]

⇒ Av. speed = 0.1/(5/1200)

⇒ Av. speed = 0.1 × 1200/5

⇒ Av. speed = 120/5

⇒ Av. speed = 24 km/h

∴ Average speed of dolphin = 24 km/h [Ans.]

Answer 2

CORRECT QUESTION:

A dolphin swims in a swimming pool from one end to another . if length of swimming pool is 50m and the dolphin is moving with a speed of 20km/h and returning with a speed of 30km/h . Find the avg speed of the dolphin in km/h

GIVEN:

• Length of swimming pool = 50m
• Travelling speed of dolphin = 20km/h
• Returning speed of dolphin = 30km/h

TO FIND:

• Average speed

SOLUTION:

Converting m → km

50m → km

To convert we have to multiply with 10-³

50 × 10-³ = 0.05km

Let , the time taken by the dolphin be x

Total distance = travelling distance + returning distance

Total distance = 50 + 50 = 0.05 + 0.05

Total distance = 0.1 km

We know that

Speed = distance/time

20 = 0.05/x

x = 0.0025

________________

30 = 0.05/x

x = 0.0016

Hence,

→ Time taken for travelling = 0.0025

→ Time taken for returning = 0.0016

Total time = 0.0025 + 0.0016 = 0.0041

_____________________________

Now,

Average speed = Total distance/Total time

Avg speed = 0.1 / 0.004

Average speed = 24 km/h

Hence, average speed = 24km/h