Problem 69.

An automobile traveling 90 km/h overtakes a 1.5-km-long train traveling in the same direction on a track parallel to the road. If the train's speed is 70 km/h,

(a) how long does it take the car to pass it, and

(b) how far will the car have traveled in the time?

Solution:

It is easier to solve this problem if we introduce the relative velocity of the car (relative to the train). The velocity of the car relative to the train is (90-70) km/h=20 km/h.

In the relative description the train is not moving and the car is moving with constant speed 20 km/h.

(a) Then we can easily find the time the car needs to pass the train. It is

(b) To find the actual traveled distance of the car we just need to multiply the traveled time (0.075 h) by the actual speed of the car: