Question

An athlete running a race completed three quarters of the journey with 40kph and rest one quarter with 20kph . Calculate the avg. speed​

Answer 1

ANSWER

Quarters run by athlete = 4

Speeds in first three quarters = 40 kph

Speed in last quarter = 20 kph

Average speed = total distance / time

But we neither have time nor distance.

So,

we will add speeds in all quarters and divide it by total no. of quarters.

= ( 40 + 40 + 40 + 20 )/4

= 140/4

= 35 kph

So, average speed in kph will be 35kph.

To change it in standard form i.e m/s, we have to multiply it by 5/18

So,

35 × 5/18

= 9.72 m/s

Answer 2

Answer:   32 kph

Explanation:

Let the total distance be x km.

Now,

As per given,

Three quaters of journey covered with a speed of 40 kph. Or,

3x/4 distance is covered with a speed of 40 kph.

Time taken to cover this distance,

t₁ = distance/speed

t₁ = (3x/4)/40

t₁ = 3x/160.

After that,

Rest x/4 distance is covered with a speed of 20 kph.

Time taken to cover this distance,

t₂ = distance/speed

t₂ = (x/4)/20

t₂ = x/80.

t₂ = 2x/160

Total time taken = t₁ + t₂

                           = 3x/160 + 2x/160

                            = 5x/160

                            = x/32 hr.

Now, We know that;

Average speed  = Total distance/Total time taken

                           = x/(x/32)

                           = 32 kph