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

Answer 1

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. $averagespeed=\frac{totaldis\tan cetraveledbyabody}{totaltimetaken}$.
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. $averagevelocity=\frac{totaldisplacementbyabody}{totaltimetaken}$

Step 2: Find the average speed

Let $V_s$ be the average speed of the body.

Now,

$V_s$$=\frac{totaldis\tan cetraveledbyabody}{totaltimetaken}=\frac{180m}{\left(1\times 60\right)sec}=3m/s.$

$or{V}_s=3m/s$

Step 3: Find the average velocity

Let $V_v$ be the average velocity of the body.

now,

$$\begin{gathered} V_v=\frac{totaldisplacementbyabody}{totaltimetaken}=\frac{0m}{\left(1\times 60\right)sec}=0 \\ or{V}_v=0. \end{gathered}$$

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