# (Momentum) Investigation of MTR train crash

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#1
On 18 March 2019, two MTR trains (A187/A112 and A131/A218) collided head-on near Central Station at 2:45 am during a test run. Each train has a weight of 300 tonnes. Train A187/A112 was moving at 35 km/h and A131/A218 was moving at 40 km/h.
1. Find the combined momentum of the trains, given that they move off together.
2. Find the speed of the trains after the collision.
3. Find the force exerted by each train.
4. After the collision three carriages (A131, D652 and C451) were damaged severely. The collision only lasted for 0.3 seconds, but why did the three carriages fall off the track?
5. 'The outbound train should wait for the inbound train to enter the station before it leaves.' Do you agree?
Last edited by 8013; 1 year ago
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1 year ago
#2
(Original post by 8013)
On 18 March 2019, two MTR trains (A187/A112 and A131/A218) collided near Central Station at 2:45 am during a test run. Each train has a weight of 300 tonnes. Train A187/A112 was moving at 35 km/h and A131/A218 was moving at 40 km/h.
1. Find the combined momentum of the trains, given that they move off together.
2. Find the speed of the trains after the collision.
3. Find the force exerted by each train.
4. After the collision three carriages (A131, D652 and C451) were damaged severely. The collision only lasted for 0.3 seconds, but why did the three carriages fall off the track?
5. 'The outbound train should wait for the inbound train to enter the station before it leaves.' Do you agree?
unclear from the text whether the collision was head to head (i.e. trains travelling in opposite directions) or head to tail (i.e. trains travelling in the same direction at different speeds)
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#3
The trains collided head-on, after editing.
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1 year ago
#4
(Original post by 8013)
The trains collided head-on, after editing.
OK they're travelling in opposite directions so I'd convert the masses and velocities to SI units and calculate the momentum of each train just before impact...
In the absence of any other information I'd assume* the trains had an inelastic collision and stuck together and ending up travelling together with the same velocity - this collision will of course obey conservation of momentum.

* trains are in my experience crunchy rather than bouncy

you'll be able to do 3 with the information in 4 about the duration of the collision...
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