Question : In a journey of three unequal laps, a car covers a distance of 200 km in 4 hr in the first lap, while another 162 km at the speed of 15 m/s in the second lap. It covered the remaining distance of the final lap in 4 hr such that the average speed of the car for the entire journey was 50 km/hr. What was the speed of the car on the third lap of the journey?
Option 1: 47 km/hr
Option 2: 52 km/hr
Option 3: 42 km/hr
Option 4: 45 km/hr
Correct Answer: 47 km/hr
Solution :
The concept used here is that the average speed is the total distance travelled divided by the total time taken.
Speed in the second lap = 15 m/s = $\frac{15×18}{5}$ km/hr = 54 km/hr
Time taken in second lap = $\frac{162}{54}$ hrs = 3 hrs
The total time taken = 4 + 3 + 4 = 11 hrs
Total distance = Average speed × Total time = 50 × 11 = 550 km
So, the distance covered in the third lap = 550 - 200 - 162 = 188 km
The speed in the third lap = $\frac{188}{4}$ = 47 km/hr
Hence, the correct answer is 47 km/hr.
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