Correct Answer - Option 2 : 16 s
Given:
Speed of train = 72 kmph
Time = 20 seconds
Speed of car = 18 kmph
Formula used:
Speed = Distance / time
1 kmph = 5/18 m/s
Calculations:
Calculating length of train
⇒ 72 kmph = 72 × 5 / 18 m/s
⇒ Speed of train = 20 m/s
⇒ length of train = Speed × Time
⇒ length = 20 × 20
⇒ Length of train = 400 m
Now, calculate relative speed
⇒ car is moving in opposite direction as train hence relative speed = 72 + 18
⇒ Relative speed = 90 kmph
⇒ Relative speed = 25 m/s
⇒ Time taken to cross car = 400 / 25
⇒ Time taken = 16 sconds
∴ Train takes 16 seconds to cross the car