# Homework Help: Circular motion question

1. Jun 9, 2012

### sydboydell31

A turntable is rotating at a constant angular velocity of ω = 4.0 rad/s in the direction of a clockwise fashion. There is a ten-cent coin on the turntable, at a distance of 5 cm from the axis of rotation.

(a) Which one of the following options below correctly identifies the direction in which the angular velocity vector is pointing?

A Clockwise
B Anti-clockwise;
C Into the page;
D Out of the page.

(b) Calculate the radial (centripetal) acceleration at the position of the ten-cent coin. Indicate the direction of this acceleration.

(c) Calculate the minimum coefficient of static friction between the coin and the turntable. Assume the coin does not slip.
Consider the time interval during which the turntable is accelerated initially from rest to its final angular velocity (ωf = 4.0 rad/s) . This is achieved with a constant angular acceleration (α) for 0.5 s.

(d) In units of rad/s2 what is the value of α?

(e) Calculate the tangential acceleration at the position of the coin?

(f) Find an expression for the magnitude of total acceleration of the coin in terms of α and ω and use this to determine the maximum total acceleration experienced by the coin.

Can someone please help me with this question? and i'm always confused between angular momentum and angular velocity, i know the first answer is "into the page" because of the right hand rule, but why?? I know it because the text book says it, but it didn't say why is it in that particular direction.

Thanks guys

2. Jun 9, 2012

### Villyer

Does your book explain how to use the right hand rule?

3. Jun 9, 2012

### Same-same

Angular momentum (L) = the cross product of the displacement vector and linear momentum vector.
L=$\stackrel{\rightarrow}{r}$ x $\stackrel{\rightarrow}{p}$
(I'd memorize how to compute a cross product, it can end up being very useful. )
A more convenient way of writing it may be
L$_{r}$=I$_{r}$ω$_{r}$ where r is a direction on an axis.

BTW, this might get more responses if you asked the mods to move it to introductory physics.