# Circular Motion and magnitude

1. Jan 27, 2010

Hi all,

I'm having a very difficult time with this problem. I know that the magnitude stays the same and it involves uniform circular motion, but I just can't seem to figure out how to begin the problem or what formula to use. I would really appreciate any kind of help.

A wall clock has a minute hand with a length of 0.47 m and an hour hand with a length of 0.24 m. Take the center of the clock as the origin, and use a Cartesian coordinate system with the positive x axis pointing to 3 o'clock and the positive y axis pointing to 12 o'clock. What is the magnitude of the acceleration of the tip of the minute hand of the clock?

I also need to express it as a fraction of the magnitude of free-fall acceleration g.

Again thank you all very much, any kind of help would be so much help.

2. Jan 27, 2010

### Staff: Mentor

What is the equation for the centripital acceleration of an object (the tip of the clock hand) as a function of radius and velocity?

3. Jan 27, 2010

Centripetal acceleration's equation is but I've tried plugging the numbers into that equation and can't seem to get it right.

a= V^2/r

4. Jan 27, 2010

### Staff: Mentor

There's another form of that equation in terms of omega. What is the omega of a minute hand on a clock?

5. Jan 27, 2010

I've never done anything with omega unfortunately. But right now I have this:

a= ((2*pi*.47)/3600)^2/.47

6. Jan 27, 2010

### Staff: Mentor

Be sure to show units in your equations -- it helps understandability and helps avoid mistakes.

Here's a page that should help you understand omega and uniform circular motion better:

http://en.wikipedia.org/wiki/Uniform_circular_motion

.

7. Jan 27, 2010

Thank you very much for the help. I also just do not understand what the second statement, "express it as a fraction of the magnitude of free-fall acceleration g." is looking for.

8. Jan 27, 2010

### Staff: Mentor

The magnitude of acceleration due to gravity at the surface of the Earth is generally called "g". Like you feel 1g while standing, and can feel higher g's when stunt flying, etc. Do you know the numerical value of 1g? It's in units of m/s^2.

9. Jan 27, 2010

Yes, 9.81. So would it be:

3.86 E-4/9.81 ?

10. Jan 27, 2010