# Homework Help: Angular rotation velocity and acceleration

1. Nov 8, 2011

### stau40

1. The problem statement, all variables and given/known data
A small object with mass 3.55 kg moves counterclockwise with constant speed 1.55 rad/s in a circle of radius 2.70 m centered at the origin. It starts at the point with position vector 2.70 m. Then it undergoes an angular displacement of 8.50 rad.

2. Relevant equations
v=ωr
a=rω^2

3. The attempt at a solution
I've calculated the new position vector of -1.63i + 2.16j and know it's in the second quadrant at 127 degrees but can't get the correct answer of -3.34i + (-2.52)j m/s for it's velocity. The equation I'm using for i is 2.7*sin(127+90) and I'm using 2.7*cos(127+90) for j and neither of these end up and the correct answer. What am I doing wrong?
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

2. Nov 8, 2011

### Simon Bridge

You described the situation, but have not given the question.

Have you been asked to give the tangential velocity in cartesian co-ordinates?

1st draw the situation.

The angle of the velocity is $\pi/2$ around from this - use the drawing to figure out which way. Draw it in. Choose the easy angles on the sketch to work out the components.