Wei zi sheng ren tie he

Let the train speed be v and the train length be s.

A, it takes 80 seconds for the whole train to get on the bridge completely, so the calculation distance should be calculated from the end of the train getting on the bridge completely, so

( 1080-s)/v=80

It takes 100 second for the train parking space to leave the bridge, that is, it takes 100 second for the train running bridge length plus its own bus length, so,

( 1080+s)/v= 100

Solve two equations to get S =120mV =12m/s.

Second, the train speed is constant and the equation can be established.

( 1080-s)/80 =( 1080+s)/ 100

You can also get s =120mv =12m/s.