Question

Two trains leave a city at 1 P.M. One train goes north at a constant rate of 75 mph. The other goes south at a constant rate of 63 mph. At what time will the trains be 621 miles apart?

Answer 1

Solution:

At 5:30 PM the distance between the train will be 621 miles.

Explanation:

We have been given that one train goes north and other train gores south. It means they are moving in opposite direction.

When two body moving in opposite directions then the relative velocity is the sum of their individual velocities.

Therefore, the relative speed is given by

$v=75+63 = 138 mph$

Now, the distance between the train is 621 miles. Hence, using the relation between speed, time and distance, we have

$\text{Speed}=\frac{\text{Distance}}{\text{Time}}\\\\138=\frac{621}{t} \\\\t=\frac{621}{138}\\\\t=4.5$

Thus, at 5:30 PM the distance between the train will be 621 miles.