# Homework Help: Rotational Motion

1. Aug 1, 2008

### dixonewman

1. The problem statement, all variables and given/known data
A rock of mass m=2kg is tied to a string of length r=4m is rotating at a constant rate and subject to a centripetal force Fc=32N.

Find the:
a)Centripetal acceleration

b)Angular velocity

c)Angular momentum

2. Relevant equations

a) Ac=V2T/R (Fc=V2T/R; so, V2T=Fc x R/m?)

c) l = mvTr

3. The attempt at a solution

a) 32 x 4/2 = 64[m2/s]

b) V2T = 64, so VT = 8; 8/4 = 2 [rad/s]

c) 2 x 8 x 4= 64[kg x m2/s]

I know this is simple stuff, but I'm new to physics, and just wanted to double-check that I'm getting my formulas right. Thanks everyone!

2. Aug 1, 2008

### rock.freak667

Use Newton's 2nd law here.
$$F_{centripetal}=ma_{centripetal}$$

This is correct. You could have also used $F=m \omega^2r$ if you wanted.

[/QUOTE]

This looks good as well.

I know this is simple stuff, but I'm new to physics, and just wanted to double-check that I'm getting my formulas right. Thanks everyone![/QUOTE]

3. Aug 1, 2008

### dixonewman

Wait, it looks like I may have jumbled up my formulas...

If V2T=Fc x R/m (is this formula correct?), if so, then V2T = 64;

Ac=V2T/R so 64/4 = 16 [m/s2]

Am I still missing the mark?

Last edited: Aug 1, 2008
4. Aug 1, 2008

### rock.freak667

16ms-2 should be correct