How Does Particle Motion on an XY Plane Change Over Time?

[kara]

The acceleration of a particle on a horizontal xy plane is given by a=3ti + 4tj, where a is in meters per second-squared and t is in sec. At t=0, the particle has the position vector r=(20.0m)i + (40.0m)j and the velocity vector
v=(5.00m/s)i +(2.00m/s)j. At t=4.00 s, what are its position vector in unit-vector notation and the angle between its direction of travel and the positive direction of the x axis?

 

[Locrian]

I'll say the same thing here as in the other problem: treat the axis as separate problems, solve both, then put the problem back together. By this point in class you've done 1d problems plenty - break this down into two separate 1d problems, figure out the i and j positions, then draw a picture of where the particle is and find the angle.