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 a train driver cross the bridge take?
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?

Correct answer:

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

Step-by-step explanation:

l=240 m t1=21 s t2=9 s  L=9 v L+240=21 v  L9v=0 L21v=240  Row2Row1Row2 L9v=0 12v=240  v=12240=20 L=0+9v=0+9 20=180  L=180 v=20=20 m/s
L=180=180 m
t3=l/v=240/20=12 s
t4=vv/22 L=2020/22 180=36 s
t5=v+v/22 L=20+20/22 180=12 s



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