NEETPhysicsMotion in One Dimension
Freight trains, each of length 500 m , leave a station every 10 minutes at a constant speed of 90 km/h . A car drives on a parallel road in the opposite direction at a constant speed of 60 km/h . What is the ratio of the time interval between the car meeting the front of successive trains to the time duration the car spends alongside a single train?
Options
- A50 : 1
- B31 : 1
- C30 : 1
- D3 : 10
Correct answer
C. 30 : 1
Step-by-step solution
The distance d between the heads of successive trains depends only on the train's speed and the departure period. d = v_ train T = 90 km/h ( 10 60 ) h = 15 km The relative speed between the car and the trains is v_ rel = 90 + 60 = 150 km/h . The time interval between the car meeting the front of successive trains is t₁ = d v_ rel . The time duration the car spends alongside a single train of length L = 500 m = 0.5 km is t₂ = L v_ rel . The required ratio is t₁ t₂ = d / v_ rel L / v_ rel = d L . Ratio = 15 km 0.5 km