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Question

A boy swims in a 90 m long pool. He covers 180 m in one minute by swimming from one end to the other and back along the same straight path. Find the average speed and average velocity of the boy


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Solution

Step 1: Given data

  1. The displacement of the boy is zero because after he travels he returns to his initial point of the journey, i.e, D=0.
  2. The length of the pool is L=90m.
  3. He travels 180m in 1 minute.
  4. Time of travelling, t=60sec.

Average speed and average velocity

  1. Speed is the time rate of change in distance traveled by a body. it is a scalar quantity (has only magnitude ).
  2. averagespeed=totaldistancetraveledbyabodytotaltimetaken.
  3. Velocity is the time rate of change in displacement traveled by a body. It is a vector quantity (has both magnitude and direction).
  4. averagevelocity=totaldisplacementbyabodytotaltimetaken

Step 2: Find the average speed

Let Vs be the average speed of the body.

Now,

Vs=totaldistancetraveledbyabodytotaltimetaken=180m1×60sec=3m/s.

orVs=3m/s

Step 3: Find the average velocity

Let Vv be the average velocity of the body.

now,

Vv=totaldisplacementbyabodytotaltimetaken=0m1×60sec=0orVv=0.

So, the average speed of the body is 3m/s and the average velocity of the body is zero.


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