# Relative velocity of two cars

How long does it take an automobile traveling in the left lane at 60.0 km/hr to pull along side a car traveling in the right lane at 40.0 km/hr if the cars' front bumpers are initially 100 m apart?

I know the velocity of the car in the left is 60 and the velocity of the car on the right is 40. I also know it's imperative to find the velocity of the left car in relation to the right car in order to compare their distances. I found this to be 20 km/hr. What I don't know, however, is how to find out how far the car on the right goes before the car on the left reaches it. I know time is distance divided by velocity, so I figure that if I can find this distance and divide it by 20 km/hr, I'll have the time.

I also know the answer in the back of the book .. 18.0 seconds. The question is, how do I get it?

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catchup time in hrs = 100 m/(20 km/hr) = .1 km/(20 km/hr) = ?

catchup time in secs = ?

HallsofIvy