Train A at a speed of 1,200m per minute has begun to enter a certain tunnel.
Train B of 1,500m per minute has begun to enter at the opposite side eight seconds later.
The top of train A and B came across in the middle of the tunnel.
Train B completely left the tunnel one minute 17 seconds later after train A began to enter the tunnel.
Find the length of this tunnel and the length of train B.
Answer
1600 m,
125 m
Solution
The speed per second of A and B is 1200/60 = 20 m/s and 1500/60 = 25 m/s.
It takes 160/(25 - 20) = 32 seconds for A and B to be the difference of 20 × 8 = 160m.
Therefore, the length of the tunnel is 25 × 32 × 2 = 1,600m.
Because B went along the tunnel in 1 minute 9 seconds - 8 seconds = 1 minute 9 seconds = 69 seconds, the length of B is 25 × 69 - 1600 = 125m.
Train B of 1,500m per minute has begun to enter at the opposite side eight seconds later.
The top of train A and B came across in the middle of the tunnel.
Train B completely left the tunnel one minute 17 seconds later after train A began to enter the tunnel.
Find the length of this tunnel and the length of train B.
Answer
1600 m,
125 m
Solution
The speed per second of A and B is 1200/60 = 20 m/s and 1500/60 = 25 m/s.
It takes 160/(25 - 20) = 32 seconds for A and B to be the difference of 20 × 8 = 160m.
Therefore, the length of the tunnel is 25 × 32 × 2 = 1,600m.
Because B went along the tunnel in 1 minute 9 seconds - 8 seconds = 1 minute 9 seconds = 69 seconds, the length of B is 25 × 69 - 1600 = 125m.
