Ram, standing on a railway platform, noticed that a train took 36 seconds to completely pass through the platform, which was 108 m long, and it took 12 seconds in passing him. Find the speed of the train.
- A25.2 km/h
- B18.2 km/h
- C16.2 km/h
- D20.2 km/h
Solution & Step-by-step Explanation
Let the length of the train be L metres and its speed be v m/s.
When passing Ram (a stationary point object), the train covers its own length:
Distance=L=v×12⟹L=12v— (Equation 1)
When passing the platform, the train covers its own length plus the platform length:
Distance=L+108=v×36— (Equation 2)
Substitute Equation 1 into Equation 2:
12v+108=36v
36v−12v=108
24v=108
v=
24
108
=4.5m/s
Convert the speed into km/h:
Speed=4.5×
5
18
=0.9×18=16.2km/h
When passing Ram (a stationary point object), the train covers its own length:
Distance=L=v×12⟹L=12v— (Equation 1)
When passing the platform, the train covers its own length plus the platform length:
Distance=L+108=v×36— (Equation 2)
Substitute Equation 1 into Equation 2:
12v+108=36v
36v−12v=108
24v=108
v=
24
108
=4.5m/s
Convert the speed into km/h:
Speed=4.5×
5
18
=0.9×18=16.2km/h