SOLUTION: Two cars start at a given time and travel in the same direction at average speeds of 40 kph and 55 kph. How much time will elapse before the two cars are 10 km apart?

Question 1203173: Two cars start at a given time and travel in the same direction at average speeds of 40 kph and 55 kph. How much time will elapse before the two cars are 10 km apart?
Answer by ikleyn(52852) (Show Source): You can put this solution on YOUR website!
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Physics solution

Their relative speed is 55 - 40 = 15 kilometers per hour.

In other words, the distance between them is 15*t kilometers, as a function of time.


The cars will be 10 km apart in   =  of an hour,  or in 40 minutes.    ANSWER

Algebra solution

Fast car distance from the start is   = 55*t kilometers.

Slow car distance from the start is   = 40*t kilometers.


The distance between the cars

     -  = 55t - 40t.


The distance equation

    55t - 40 t = 10  kilometers.


Simplify and find t

       15t     = 10

         t     =  =  of an hour = 40 minutes.


The same answer.

Solved.

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