Question

A car travels from stop A to stop B with a speed of 30km/h and then returns back to stop A with a speed of 50km/h. Find : Average speed of the car.

Answer 1

Answer:

37.5km/h

Explanation:

let distance travelled from a to b=x

therefore, total distance= 2x

time from a to b = x/30

time from b to a= x/50

total time= x/30+x/50= 8x/150

total time= 4x/75

average speed= total distance/total time

                         = 2x *75/4x

                          = 37.5 km/h

Answer 2

Given:

A car travels from stop A to stop B with a speed of 30 km/h

Then returns back to stop A with a speed of 50 km/h

To Find:

Average speed of the car

Solution:

We know that,

• If a body covers first half of a distance with speed v₁ and second half with speed v₂, then

$\pink{\underline{\boxed{\bf{Average\ Speed=\dfrac{2v_{1}v_{2}}{v_{1}+v_{2}}}}}}$

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It is given that car travels from stop A to stop B and then return to stop B, that means distance travelled in going and returning is same.

So, journey of car from stop A to stop B is considered as first half and journey of car from stop B to stop A is considered as second half of the total journey.

Here,

$\longrightarrow\rm{v_{1}=30 km/h}$

$\longrightarrow\rm{v_{2}=50 km/h}$

Let the average speed of car be S

So,

$\longrightarrow\rm{S=\dfrac{2v_{1}v_{2}}{v_{1}+v_{2}}}$

$\longrightarrow\rm{S=\dfrac{2\times30\times50}{30+50}}$

$\longrightarrow\rm{S=\dfrac{2\times30\times50}{80}}$

$\longrightarrow\rm\green{S=37.5\ km/h}$

Hence, the average speed of car for given journey is 37.5 km/h.

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Additional Information

Speed

The distance covered by moving body in unit time is called speed of the body.

Average Speed

Average speed is defined as the ratio of total distance covered and total time taken.