Determine the time it take for the car and the truck to meet

[Arden]

a car starts from rest at a point 300m from a truch that is moving at a constant rate of 30m/s toward the car. IF the car accelerates at .8m/s2, determine the time it take for the car and the truck to meet.
s=300
This is what I did
Car:
Vi = 0, a = .8
Vf^2=2as = Vf=21.9

Vf=at
21.9/.8 = 27.38
t=27.38sec

Truck:
S=(V/2)t
S=(15)t
300/15 = 20
t=20

They meet after (27.38 -20) = 7.38 seconds.

The answer given is 8.94seconds. Not sure what I am doing wrong?

 

[James R]

You assumed the truck meets the car at 300 m. It doesn't, because the truck is moving towards the car.

 

[Pyrrhus]

You will need to set up your equation such as the car will cover a distance x, which will be the distance the truck meets the car, but the truck will cover a distance x+300.

 

[mathmike]

dont you mean 300 - x

 

[Pyrrhus]

Depends on where you put your coordinate system, i put the origin on the car.

 

[Arden]

Thank you all for your help - Arden