Kinematics problem that i cant seem to resolve

[adoule]

Homework Statement

A truck starts from rest and accelerates at 1 M/S*2 . 4 s later, a car accelerates from rest at the same starting point with an acceleration of 2.7 M/S*2 .

Where and when does the car catch the truck?

Homework Equations

i have tried s=ut + (1/2)at^2

The Attempt at a Solution

In 4 seconds, truck travels a distance of 0 (4) + (1/2) (1) (4)^2 = 0 + 8 = 8

now, when car starts, truck is already 8 m ahead of it.

Suppose they meet at time lapse of t seconds after car starts.
So, car travels 8 m more than the truck in t seconds.
distance traveled by car in t seconds = dist travelld by truck in t seconds + 8

0 (t) + (1/2) (2.7) (t)^2 = 0 ( t) + (1/2) (1) (t)^2 + 8

==> (t)^2 = (160) / 17
t = 3.06

hence, car catches truck at 4 + 3.06 = 7.06 seconds after truck starts.
distance traveled by car = 0 (7.06) + (1/2) (4) ( 160/17) = 18.8 metres, but that's not the anwser :s

 

[lewando]

Yo, why 2 threads? I know, in theory it should speed things up .

 

[RTW69]

The distance the truck travels will equal the distance the car travels. Try setting your distance formulas equal to each other and see what you get.