Two trains

Through the bridge, long l = 240m, the train passes through the constant speed at time t1 = 21s. A train running along the traffic lights at the edge of the bridge passes the same speed at t2 = 9s.

a) What speed v did the train go?
b) How long did it take for a train driver to cross the bridge?
c) What is the L train length?
d) How long will it take for a train to overtake in the same direction with the same length but half the speed?
e) How long will it take for a train to overtake in the opposite direction with the same length but half the speed?

Result

v =  20 m/s
L =  180 m
t3 =  12 s
t4 =  36 s
t5 =  12 s

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