Question

A body travels half the distance with speed of
20 m/s and the other half with speed of
30 m/s. The average speed of the body
during whole journey is :
A
zero
B
24 m/s
с
23 m/s
None of these​

Answer 1

${\huge{\boxed{\mathcal{\red{Answer}}}}}$

Average speed = B) 24m/s

${\huge{\boxed{\mathcal{\red{Explanation}}}}}$

Let the total distance travelled by body be x m.

Now it is given that :

In first case :

Distance travelled by body = x/2

Speed = 20m/s

Time = ?

In second case :

Distance travelled by body = x/2

Speed = 30m/s

Time = ?

Now for a body the average speed = total distance travelled / total time taken.

Now let the time taken in first case be

$= t_1$

Now time = distance/speed

So the time taken by the body in first case is :

$= \frac{ \frac{x}{2} }{20}$

$= \frac{x}{40}$

Now let the time taken by body in second case :

$= t_2$

So the time taken by body is second case is :

$\frac{ \frac{x}{2} }{30}$

$= \frac{x}{60}$

Therefore we got the total time taken by body in whole journey :

$t_1 + t_2$

$= \frac{x}{40} + \frac{x}{60}$

$= \frac{100x}{2400}$

Now the average speed of body is :

$= \frac{x}{ \frac{100x}{2400} }$

$= \frac{ x \times 2400}{100x}$

$= \frac{2400}{100}$

$= 24$

Therefore the average speed of body is 24m/s.

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BY√\____________ SCIVIBHANSHU

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