Solving the Speedster Puzzle: Calculating Time to Catch Up

[Sar06]

I am stuck on this problem...
A speeding motorist traveling 120 km/h passes a stationary police officer. The officer immediately begins pursuit at a constant acceleration of 10.2 km/h/s (note the mixed units). How much time will it take for the police officer to reach the speeder, assuming that the speeder maintains a constant speed?

 

[hotvette]

Do you have any equations of motion you are suppose to use?

 

[Sar06]

I know 3 equations of motion, but up until now I have only been looking for one variable or working with only one moving object... I'm not quite sure how to incorporate both moving objects into the equations I have. Could someone possibly lead me toward the process for finding the solution? Thanks.

 

[cscott]

You know the distance will be the same so

d = vt
d = 1/2at^2

You can equate those

vt = 1/2at^2

Fix your units and solve.

 

[Sar06]

got it!

thank you so much.