The two trains run on two parallel tracks at a speed of 10 m / s and 15 m / s. Train lengths are 120 m and 150 m

| January 8, 2021 | education

The two trains run on two parallel tracks at a speed of 10 m / s and 15 m / s. Train lengths are 120 m and 150 m, respectively. Determine the time during which the second train overtakes the first. With which body did you associate the frame of reference. What other body can you associate it with?

V1 = 10 m / s.
V2 = 15 m / s.
L1 = 120 m.
L2 = 150 m.
t -?
Since the trains move in the same direction, the speed of the second train relative to the first V21 will be the difference: V21 = V2 – V1, where V2, V1 are the speeds of the second and first trains relative to the earth’s surface, that is, relative to a stationary frame of reference.
Since overtaking begins when the head of the second train is flush with the tail of the first train, and ends when the tail of the second is flush with the head of the first. To overtake the second train must travel a distance L equal to the sum of the lengths of the first L1 and the second train L2: L = L1 + L2.
The overtaking time t will be the ratio: t = L / V21 = (L1 + L2) / (V2 – V1).
t = (120 m + 150 m) / (15 m / s – 10 m / s) = 54 s.
Answer: the second train overtakes the first in time t = 54 s.



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