A car moves with a speed of 30 km/h–1 for half an hour, 25 km/h–1 for one hour and 40 km/h–1 for two hours. Calculate the average speed of the car.
Answers
Let us find the distances first.
□ Car moves with 30 kmph for half an hour. This means 30 x 1/2 = 15 km
□ Car moves with 25 kmph for an hour. This means 25 x 1= 25 km
□ Car moves with 40 kmph for half an hour. This means 40 x 2 = 80 km
So, the total distance is 80 + 25 + 15 = 120
On, adding the hours, we have: 0.5 + 1 + 2 = 3.5 hours
□ Now we know that, S = D / T
Therefore, S = 120 / 3.5
Ans. 34.2 kmh is the average speed of the car.
Solution :
First case :
Speed = 30 km/hr .
Time = 1/2 hr .
Distance = Speed × time
⇒ Distance = 30 km/hr × 1/2 hr
⇒ Distance = 15 km
Second case :
Time = 25 km/hr
Speed = 1 hr
Distance = speed × time
⇒ Distance = 25 km/hr × 1 hr
⇒ Distance = 25 km
Third case :
Time = 2 hrs .
Speed = 40 km/hr
Distance = speed × time
⇒ Distance = 40 km/hr × 2 hr
⇒ Distance = 80 km
Total distance = 80 km + 25 km/hr + 15 km/hr
⇒ Total distance = 120 km/hr
Average speed = total distance / total time
⇒ Average speed = 120 km / ( 1/2 + 1 + 2 ) hr
⇒ Average speed = 120 km / 7/2 hr
⇒ Average speed = 240/7 km/hr
The average speed ≈ 34.29 km/hr .