Question

A car travels 40 km at a uniform speed of 30 km/h and the next 30 km at a unform speed of 50km/hr find ots average speed

Answer 1

As per given condition, a car travels 40 km at a uniform speed of 30 km/h and the next 30 km at a unform speed of 50km/hr.

We have to find the average speed of the car.

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

Total distance covered by the car = Distance covered by car in (first half + second half)

= (40 + 30) km

= 70 km

Also,

Time = Distance/Speed

Case 1)

t1 = 40/30 = 1.3 hr

Case 2)

t2 = 30/50 = 0.6 hr

Total time taken = t1 + t2

= (1.3 + 0.6) hr

= 1.9 hr

Average speed = 70/1.9 = 36.84 km/hr

Therefore, the average speed of the car is 37 km/hr.

Shortcut Method

Average speed = (2 × S1 × S2)/(S1 + S2)

= (2 × 30 × 50)/(30 + 50)

= 3000/80

= 37 km/hr (approx.)

Answer 2

Given:

• Speed for first 40 km = 30km/h
• Speed for next 30km = 50km/h

To find:

• Average speed

Solution:

Firstly finding total time

Total time = t1 + t2

Time = distance/speed

♦ t1 = 40/30

♦ t1 = 4/3

→ t2 = 30/50

→ t2 = 3/5

Now,

Total time = 4/3 + 3/5

Total time = 29/15

____________________

Total distance = 40 + 30

Total distance = 70km

____________________

Average speed = Total distance/Total time

Avg speed = 70/29/15

Avg speed = 36.206 ≈ 37

Henec , average speed = 37 km/h