# Homework Help: Circular motion

1. Nov 12, 2013

### toljin123

1. The problem statement, all variables and given/known data
A body of mass 2kg performs circular motion about a point O. The radius of the circle is 0.4m and the mass completes 20 revolutions per minute.Calculate:

1) the angular veloicty.
2)the linear velocity.
3) the centripetal acceleration,and
4) the kinetic energy
5) Draw a diagram showing the position vector, the velocity vector and acceleration vector at time t=0.5s

1) = 2pi/3
2)(0.4) * (2pi/3) = 0.8377
3)(2pi/3)^2(0.4) = 1.754
4)1/2(2)(0.8377)^2 = 0.701

I have completed 1-4, but i having some trouble doing number 5. Any help would be great :)

Last edited: Nov 12, 2013
2. Nov 13, 2013

### ehild

Hi Toljin, welcome to PF !

Draw a circle - is it ready? Place a dot on the circumference, indicating the initial position of the body (we assume it small with respect to the radius), and also its position 0.5 s later.

The position vector is just a vector drawn from the centre of the circle to the body.

What do you know about the velocity vector?
tangent to the circle
The angular velocity is constant, so you get only centripetal acceleration. What is its direction?

ehild