# Homework Help: Birds in uniform cirular motion

1. Oct 16, 2008

### iluvphys

Hi friends,

1. The problem statement, all variables and given/known data
Birds of prey rise up and down on thermals. A bird completes circle of radius 10m every 6s and rises vertically at a rate of 4.0 m/s. Assume uniform acceleration. Find

a)speed of bird relative to ground
b)magnitude of acceleration
c)direction of birds acceleration
d)angle between birds velocity vector and horizontal.

2. Relevant equations

ar = v^2/r

3. The attempt at a solution
I have got answers for a to c. a) 11.2 m/s b) 11 m/s^2 c) 0°

But I cant really figure out how i can measure the angle.

Could it be tan-1 = 4/11.2 = 19.65?

God in the past few days I have been dreaming about angles.

2. Oct 16, 2008

### LowlyPion

w = 2*π*f =v/r

v = 2*π*r*f

There is also the acceleration of 4 m/s2 in the z direction don't forget.

As to your dreams, maybe try and forget the acute ones? There are plenty of others out there.

3. Oct 16, 2008

### iluvphys

Hi Pion, thanks for the reply.

What do you mean by w = 2*π*f =v/r

v = 2*π*r*f?
What is w, n, and f?

Is this how I get the angle?

Also 4m/s is the velocity not the acceleration :-)

4. Oct 16, 2008

### iluvphys

Yeah.
I got the answer but I did it in a different way.

I separated the vector into its components vx and vy.

vx = 4 vy = 10.47

then: tan-1 = 4/10.47 = 20.something!

Thanks anyway!