Question

5.
A car covers first 100 km of his journey at 50 km/h, next 50 km at 40 km/h and last 75 km in 14 h.
Find the average speed of the whole journey.​

Answer 1

Given :-

• A car covers first 100 km of his journey at 50 km/h, next 50 km at 40 km/h and last 75 km in 14 km/h.

To find :-

• Average speed of whole journey

Solution :-

• In first case

A car covers first 100 km of his journey at 50 km/h

• Distance (D1) = 100km
• Speed = 50 km/h

As we know that

→ Time = distance/speed

→ T1 = 100/50

→ T1 = 2 hours

• In second case

A car covers 50 km of his journey at 40 km/h

• D2 = 50km
• Speed = 40km/h

→ Time = distance/speed

→ T2 = 50/40

→ T2 = 5/4

→ T2 = 1.25 hours

• In third case

A car covers 75 km of his journey at 14 km/h

• D3 = 75km
• Speed = 14km/h

→ T3 = 75/14

→ T3 = 5.35 hours

Now,

→ Average speed = Total distance travelled/total time

→ Average speed = D1 + D2 + D3/T1 + T2 + T3

→ Average speed = 100 + 50 + 75/2 + 1.25 + 5.35

→ Average speed = 225/8.6

→ Average speed = 26.16 km/h

Hence,

• Average speed of a car is 26.16km/h