Question

a car covers 30 km in 30 min and the next 30 km is 40 min.Calculate the average speed for the entire journey

Answer 1

average speed = total distance/ total time
30 min= 30/60 hr = 1/2 hr
40 min= 40/60 hr = 2/3 hr
total time= 1/2+2/3= 7/6 hr
total distance= 30 km+ 30 km= 60 km
average speed= 60/7/6= 60*6/7= 360/7= 51.42 km/hr

Answer 2

Given: Distance covered, d₁ = 30 km and d₂ = 30 km

           Time taken, t₁ = 30 min and t₂ = 40 min

To Find: Average speed of the entire journey, S.

Solution:

To calculate the average speed of the car, the formula used:

• Speed = Distance / Time

•  Average speed, S = Total distance covered/ total time taken

• S =  d₁ +d₂ /  t₁ + t₂

 here, d₁ = 30 km and d₂ = 30 km

           t₁ = 30 min and  t₂  = 40 min

Converting minute into hour:

As, 1 hour = 60 minutes

So, 30 min = (1/60) x 30 = 1/2 hr

and in 40 min = (1/60) x 40 = 2/3 hr

Total distance = d₁ +d₂ = 30 +30 = 60 km

Total time taken = t₁ + t₂ = 1/2 + 2/3 = 7/6 hr

Applying the above formula-

S = 60/ (7/6)

S = (60 x 6)/ 7

S = 360/7

S = 51.4 km/hr

Hence the average speed of the car for the entire journey is 51.4km/hr.