Answer:
The Man needs to run at 9 mph
Step-by-step explanation:
Let M stand for the man's speed in mph. When the man
runs toward point A, the relative speed of the train with respect
to the man is the train's speed plus the man's speed (45 + M).
When he runs toward point B, the relative speed of the train is the
train's speed minus the man's speed (45 - M).
When he runs toward the train the distance he covers is 2 units.
When he runs in the direction of the train the distance he covers
is 3 units. We can now write that the ratio of the relative speed
of the train when he is running toward point A to the relative speed
of the train when he is running toward point B, is equal to the
inverse ratio of the two distance units or
(45 + M) 3
----------- = ---
(45 - M) 2
90+2 M=135-3 M
⇒5 M = 45
⇒ M = 9 mph
The Man needs to run at 9 mph
Answer: 9 mph
Step-by-step explanation:
Given that a man walking on a railroad bridge is 2/5 of the way along the bridge when he notices a train at a distance approaching at the constant rate of 45 mph .
If the man tend to run in the forward direction, he will cover another 2/5 before the train reaches his initial position. The distance covered by the man will be 2/5 + 2/5 = 4/5
The remaining distance = 1 - 4/5 = 1/5
If the man can run at a constant rate in either direction to get off the bridge just in time before the train hits him, the time it will take the man will be
Speed = distance/time
Time = 1/5d ÷ speed
The time it will take the train to cover the entire distance d will be
Time = d ÷ 45
Equate the two time
1/5d ÷ speed = d ÷ 45
Speed = d/5 × 45/d
Speed = 9 mph
