Two trains of length 120 m and 90 m run in the same direction with speeds of…
2017
Two trains of length 120 m and 90 m run in the same direction with speeds of 72 km/hr and 54 km/hr respectively. The approximate time taken by the longer train to cross the shorter one will be:
- A.
42 seconds
- B.
65 seconds
- C.
95 seconds
- D.
115 seconds
Attempted by 57 students.
Show answer & explanation
Correct answer: A
Solution: Use relative speed because the trains move in the same direction.
Step 1: Convert speeds to m/s. 72 km/h = 72 × 5/18 = 20 m/s; 54 km/h = 54 × 5/18 = 15 m/s.
Step 2: Find relative speed (difference) = 20 m/s − 15 m/s = 5 m/s.
Step 3: Total distance to be covered for one train to completely pass the other = 120 m + 90 m = 210 m.
Step 4: Time = distance / relative speed = 210 m / 5 m/s = 42 s.
Answer: 42 seconds