# Homework Help: Uniform circular acceleration and direction

1. Sep 19, 2008

### anubis01

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 8m every 5s and rises vertically at a rate of 3.0 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 found the answer to a be 10.5 m/s, the answer to b is 12.6 m/s^2

c)at/ar=tan^-1(3/12.6)=13.3 degrees

d) I'm not sure how to proceed for this equation.

Any help is greatly appreciated and thank you for your time.

2. Sep 19, 2008

### Kurdt

Staff Emeritus
For part c the bird is in uniform circular motion. The bird is rising at a rate of 3m/s is not an acceleration.

For part d you have the vertical component of velocity and the component tangent to the circular motion. Find the resultant.

3. Sep 19, 2008

### anubis01

Thanl you very much sir for the help and I finally got d :). HOwever I'm still a little bit confused about c. Centripetal acceleration has the same magnitude but varying direction so how am I supposed to find the direction of the birds acceleration above the horizontal.

4. Sep 19, 2008

### Kurdt

Staff Emeritus
C says nothing about direction above the horizontal, it merely asks for direction as you have typed it.

5. Sep 19, 2008

### anubis01

I see, thanks again.