Question

A body covers half the distance with a speed of $20m/s$ and the other half with $30m/s$. The average speed of the body during the whole journey is

• A. Zero
• B. $24m/s$
• C. $25m/s$
• D. None of the above

Answer 1

The correct option is B $24m/s$

Given that,

A body covers half the distance with a speed of $20m/s$ and the other half with $30m/s$.

Let us considered the total distance is $2nm$.

A body covers $n$ distance with a speed of $20m/s$

Then, the time is

$t_1=\frac{n}{20}$......(I)

The other $n$ distance with a speed $30m/s$.

Then, the time is

$t_2=\frac{n}{30}$....(II)

Now, the total time is

$t=t_1+t_2$

$t=\frac{n}{20}+\frac{n}{30}$

$t=\frac{5n}{60}s$

The average speed is

$\Delta v=\frac{2n}{\frac{5n}{60}}$

$\Delta v=24m/s$

The average velocity is $24m/s$

Hence, The correct option is B.