A car travels first half distance between two places with a speed of 40 km/hr…
2023
A car travels first half distance between two places with a speed of 40 km/hr and rest of the half distance with a speed of 60 km/hr. The average speed of the car is:
- A.
68 Km/hr
- B.
48 Km/hr
- C.
28 Km/hr
- D.
58 Km/hr
Attempted by 81 students.
Show answer & explanation
Correct answer: B
Answer: 48 km/hr
Take the total distance as 2 km, so each half-distance is 1 km.
Time for first half = distance/speed = 1/40 hr; time for second half = 1/60 hr.
Total time = 1/40 + 1/60 = (3 + 2)/120 = 5/120 = 1/24 hr.
Average speed = total distance / total time = 2 / (1/24) = 48 km/hr.
Shortcut: For equal distances, the average speed is the harmonic mean: 2*v1*v2/(v1+v2) = 2*40*60/(40+60) = 48 km/hr.