A car travels at a rate of 30 Kmh for 5min and then at 40 Kmh for 10 min. Find (a) the total distance travelled by the car and (b) the average speed of the car.
Answers
Given :
A car travels at a rate of 30 km/hr for 5min and then at 40 km/hr for 10min.
To Find :
Total distance travelled and average speed of the car.
Solution :
First of all we need to convert unit of time into hrs. We know that, 60 min = 1 hr
∴ t₁ = 5 min = 5/60 = 1/12 hr
∴ t₂ = 10 min = 10/60 = 1/6 hr
❒ Total distance travelled by the car :
Speed is defined as the ratio of distance travelled to the time taken
- Speed = Distance / Time
Therefore, distance = speed × time
➙ d = d₁ + d₂
➙ d = (v₁ × t₁) + (v₂ × t₂)
➙ d = (30 × 1/12) + (40 × 1/6)
➙ d = 2.5 + 6.67
➙ d = 9.17 km
❒ Average speed of the car :
Average speed is defined as the ratio of total distance travelled to the time taken.
- It is a scalar quantity having only magnitude.
- SI unit : m/s
Total distance travelled = 9.17 km
Total time taken = 1/12 + 1/6 = 1/4 hr
➠ Vav = d / t
➠ Vav = 9.17 / (1/4)
➠ Vav = 9.17 × 4
➠ Vav = 36.68 km/hr