Question

Find the average speed of a car which travels the first 30 km at a speed of 40 km h-1 and the remaining 20 km at a speed of 60 km h-1


step by step explanation .​

Answer 1

Answer:

Average = 46.15 km h-1

Step-by-step explanation:

First

30 km  @ speed of 40 km h-1

40 Km = 60 minutes

30 km = ? minutes

Time taken  = (30km X 60 minutes )/ 40 km= 45 minutes.

second

20 km @ speed of 60km h-1

60 Km = 60 minutes

20 km = ? minutes

Time taken  = (20km X 60 minutes )/ 60 km= 20 minutes.

First - 30 km - time taken 45 minutes

second 20 km - time taken 20 minutes

Total 50 km - time taken 65 minutes

Average speed

65 minutes = 50 km

60 minutes = ? km

Average speed = (60 minutes X 50 km)/ 65 minutes = 46.15 km h-1

Answer 2

Given :

• A car which travels the first 30 km at a speed of 40 km/h and the remaining 20 km at a speed of 60 km/h.

To Find :

• Average speed = ?

Solution :

For first 30 km :

• Distance (s) = 30 km
• Speed (v) = 40 km/hr
• Time (t) = ?

→ Time = Distance ÷ speed

→ Time = 30 ÷ 40

→ Time = 3/4 hours

For next 20 km :

• Distance (s) = 20 km
• Speed (v) = 60 km/hr
• Time (t) = ?

→ Time = Distance ÷ Speed

→ Time = 20 ÷ 60

→ Time = 2/6 hours

Finding the Total distance travelled by the car :

→ Total distance = distance travelled for first 30 km + distance travelled for next 20 km

→ Total distance = 30 + 20

→ Total distance = 50 km

• Hence,the total distance travelled by the car is 50 km.

Now, Let's calculate the total time taken by the car :

→ Total time taken = 3/4 + 2/6

→ Total time taken = 0.75 + 0.34

→ Total time taken = 1.09 hours

• Hence,the total time taken by the car is 1.09 hours.

Let's find the average speed of the car :

→ Average Speed = Toatal Distance travelled ÷ Total time taken

→ Average Speed = 50 ÷ 1.09

→ Average Speed = 45.88 km/hr

• Hence,the average speed of the car is 45.88 km/hr.