Calculating Collision Time for Two Objects with Different Initial Velocities

[Speedking96]

Homework Statement

Two balls are thrown upwards from the same spot 1.15 seconds apart. The first ball had an initial velocity of 15.0 m/s and the second was 12.0 m/s. At what time do they collide?

2. The attempt at a solution

a = first ball b= second ball

For them to collide, their height must be the same:

d_a = d_b
Vi_a x t_a + (0.5)(-9.81)(t_a^2) = Vi_b t_b + (0.5)(-9.81)(t_b)²

(15 m/s) x (t) + (0.5)(-9.81)(t²) = (12 m/s)(t-1.15) + (0.5)(-9.81)(t-1.15)²

When I solve for t, I get 0.78 seconds... I know that this is incorrect. I don't know where I went wrong, it might be in how I set up the equation.

 

[Speedking96]

nvm, I've figured it out.

 

[lightgrav]

setup looks good. I would suspect a mistake in expanding the (t-1.15)² .