PS Question - Car overtaking truck

[pacer]

A car accelerates at 6 m/s^2 starting from rest. At the same time, a truck travelling at 21 m/s passes the car. How long will it take for the car to overtake the truck?

I am confused about how to set up the formulas for this type of question.

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[labqi]

I think you do it as follows
Car d=vot + 0.5at2
Truck d=vt

Since they travel the same distance d is equal for both then
vot + 0.5at2 = vt

I am not sure but that's how I would approach. Please correct me if in wrong.


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[justadream]

Distance traveled by car = distance traveled by truck

Distance traveled by car = .5 *a * t^2 = .5*6 * t^2 = 3t^2

Distance traveled by truck = 21t

3t^2 = 21t
t = 21/3

It will take 21/3 seconds.

Plug back into either equation to find distance at this point.
Distance = 21t = 21*(21/3) = 147