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?????

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James R

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

Pyrrhus

Homework Helper
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

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

Arden

Thank you all for your help - Arden

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