Question

1b.
6. A car travels first 30 km with a uniform speed of
60 km h-1 and then next 30 km with a uniform speed
of 40 km h-1. Calculate : (i) the total time of journey,
(ii) the average speed of the car.
منگنه​

Answer 1

Answer:-

Given:-

• Case¹ : Distance travelled= 30 km (s₁)

Speed = 60 km/h (v₁)

• Case² : Distance travelled= 30 km (s₂)

Speed = 40 km/h (v₂)

To Find:-

1. Total time of the journey.
2. Avg. speed of the car.

_____________...

➽ 1. Total time taken (t):-

Time taken = Time taken in case¹ + Time taken in case²

Case¹:- (t₁)

t = s/v

➠ t = 30 km/(60 km/h)

➠ t = ½ h

Case ²:- (t₂)

t = s/v

➠ t = 30km/(40 km/h)

➠ t = ¾ h

∴ Total (t) = (t₁) + (t₂)

➠ t = (½ + ¾) h

➠ t = 5/4 h (Add the frac. by taking LCM 4)

➠ t = 1.25 h ...(Ans. 1)

➽ 2. Avg. speed of the car:-

We know,

➤ Avg. speed = Total distance/Total time taken

∴ Avg. speed = (30 km + 30 km)/(1.25 h)

➠ vₐᵥ = 60 km / 1.25 h

➠ vₐᵥ = 48 km/h ...(Ans. 2)