Two moving objects; 1D; constant

[burton95]

Homework Statement

2 objects A and B.
A has a 4000 m. head start on x-axis heading to the right
V_a = 50 m/s;
V_b = 55 m/s
a_a = 0.5 m/s²
a_b = 1.0 m/s₂

need to know t in s when x_a = x_b

Homework Equations

r = r₀+vt-a(t²/2)

The Attempt at a Solution

I set each up for x_a,b in said equation and set them equal to each other.
I plugged and chugged to a quadratic equation and ended up with a horrible answer of 140.04 seconds which makes no sense and then the other answer was negative

 

[rude man]

Homework Statement

Homework Equations

r = r₀+vt-a(t²/2)

I don't think that equation's relevant! (It represents the height of something tossed straight up at initial height r₀ with initial velocity v if a = g = 9.81 m/s^2.)

Try to change the sign of the at^2/2 term?

 

[burton95]

Yeah so close...but yet so far. Thanks