Train A and B run with a fixed speed respectively.
Fig.1 shows a relation between the time from when two trains meet until they get away and the length of the part of trains overlapping.
Fig.2 shows a relation between the time from when A catches up with B until they get away and the length of the part of trains overlapping.
Answer the following questions.
(1) Find the speed per second of A.
(2) 150 m
Solution
(1) According to the graph of Fig.1, total of the speed per second of two trains is 120 / 4 = 30 m/s.
Solution
(1) According to the graph of Fig.1, total of the speed per second of two trains is 120 / 4 = 30 m/s.
According to the graph of Fig.2, difference of the speed per second of two trains is 120 / 60 = 2 m/s.
The speed per second of A is (39 + 2) / 2 = 16 m/s.
(2) Because two trains pass each other in 9 seconds, the total of the length of two trains is 30 × 9 = 270 m.
Therefore the length of longer train is 270 - 120 = 150 m.
