Solving Particle Trajectory: Speed & Direction at t=4.5s

[jimmyv12]

A particle's trajectory is described by x=((1/2)t^3 - 2t^2) and y=((1/2)t^2-2t) , where t is in s.


What is the particle's speed at t= 4.5 s?
What is the particle's direction of motion, measured as an angle from the x-axis, at t=4.5 s?

I keep geting the wrong answers >:0 , how do I go about solving this?

 

[danago]

How did you try solving this? Show us so we can explain where you went wrong.

 

[lubuntu]

Take the derivative of both.

Then solve for t = 4.5s, us these vector components to find the angle.

 

[jimmyv12]

Alright, so i don't know why I wasnt getting the right answer before(i was taking the derivatives), but I took the derivatives for x and y, then used the sqrt(x^2+y^2) to get part one. Then y=cos^-1(x/v) for part two.