Physics, asked by rakinanwar2862, 10 months ago

John runs for 10 min at a uniform speed of 9 km/h. At what speed he should run for the next 20 min, so that the average speed comes 12 km/h?

Answers

Answered by Anonymous
37

Given that, the John runs for 10 min at a uniform speed of 9 km/hr.

We have find the speed of the John with which he should run for the next 20 min, so that the average speed comes 12 km/hr.

Now,

Average speed is defined as the ratio of total distance covered with respect to total time taken.

Let's assume that the speed of the John in next 20 min is x km/hr.

Total distance covered by John = (9 + x)km

Total time taken = (10 + 20) min = 30 min = 1/2 hr.

Average speed = 12 km/hr (given)

Also,

Distance = Speed × Time

d1 = 9 × 1/6 = 1.5 km

d2 = x × 1/3 = x/3 km

Average speed = (Total distance covered)/(Total time taken)

Substitute the known values,

→ 12 = (1.5 + x/3)/(1/2)

→ 6 = 1.5 + x/3

→ 6 - 1.5 = x/3

→ 4.5 = x/3

→ 13.5 = x

Therefore, the speed of the John in next 20 min is 13.5 km/hr.

Answered by ItzArchimedes
18

Given:

  • John runs uniform speed of 9km/h for 10min

To find:

  • Speed of John for next 20 min so that average speed becomes 12km/h

Solution:

Covert min → hrs

10min → 0.16 hrs

20min → 0.33

Let distance covered by John by next 20min be x

So,

Total distance = 9km + x km

Total time = 10min + 20min = 30min = 1/2hr

Avg speed for 10min = 12km/h

Now,

Distance = speed × time

Distance 1 = 9 × 0.166 = 1.5

Distance 2 = x × 0.33 = 0.33x = x/3

Total distance = d1 + d2

→ Total distance = 1.5 + x/3

d1 + d2 = 1.5 + x/3

Now,

Average speed = d1 + d2/t1 + t2 = total distance/total time

♦ Avg speed = (1.5 + x/3)/1/2

♦ 12 = (1.5 + x/3) × 2

♦ 12 = 3 + 2x/3

♦ 36 = 9 + 2x

♦ 36 - 9 = 2x

♦ x = 25/2

x = 12.5

Hence, speed of John = 12.5km/h

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