Question

62. A car covers 1/3 distance with speed 20 km/hr and
2/3 with 60 km/h. Average speed is
A. 40 km/h
B. 50 V2 km/h
C. 36 km/h
D. 80 km/h​

Answer 1

Answer :

Given -

• 1/3 distance was covered with speed of 20 km/hr
• And 2/3 distance was covered with speed of 60 km/hr

To Find -

• Average Speed ?

Solution -

Let the whole Distance be x.

So, the Distance travelled at the speed of 20 km/hr is x/3 m.

The time taken to travel this Distance = (x/3)/20 = x/60 sec.

Now, the Distance travelled at the speed of 60 km/hr is 2x/3 m.

The time taken to travel this Distance = (2x/3)/60 = 2x/180 = x/90 sec.

Now, We know that, Average Speed = Total Distance/Total Time.

⇒ Avg. Speed = (x)/(x/60 + x/90)

⇒ Avg. Speed = x/(3x+2x/180)

⇒ Avg. Speed = x/(5x/180)

⇒ Avg. Speed = x/(x/36)

⇒ Avg. Speed = x*36/x

⇒ Avg. Speed = 36 km/hr

Hence, Average Speed = 36 km/hr.

Answer 2

Given:

• 1/3 distance with Speed of 20km/h
• 2/3 distance with Speed of 60km/h

To find:

• Average Speed

Solution:

Let the total distance be x

Finding time using

Time = distance/Speed

→ Time 1 (t1) = x/3/20 = x/60

→ Time 2 (t2) = 2x/3/60 = x/90

Total time = t1 + t2

→ total time = x/60 + x/90

→ Total time = x/36

Now,

Average Speed = Total distance/Total time

→ Avg. Speed = x/x/36

→ Avg. Speed = 36x/x

→ Avg. Speed = 36km/h

Hence average Speed of car is 36km/h , option c is your answer