# Uniform circular motion

1. Sep 17, 2006

### mbrmbrg

An astronaut is rotated in a horizontal centrifuge at a radius of 3.0 m.
(a) What is the astronaut's speed if the centripetal acceleration is 8.0g?
(b) How many revolutions per minute are required to produce this acceleration?
(c) What is the period of the motion?

I got the question all wrong, all wrong... la-la la... ROAR!!

for part a) I used the equation $a=\frac{v^2}{r}$ which rearranges into $v= \sqrt{ar}$. Plug in my values and get $v=\sqrt{(8.0)(9.81m/s^2)(3.0m)}=15.34$

This gets used for parts b and c, which is why I'd get those wrong, too...

What I did for part c) is $T= \frac{2\pi r}{v}$ $= \frac{6\pi}{15.34}$ $= 0.81$.

And part b) asks for frequency, which is 1/T so I plugged in for $f=\frac{v}{2\pi\r}$

Last edited: Sep 17, 2006
2. Sep 17, 2006

### vsage

RPM is not frequency.

3. Sep 17, 2006

### mbrmbrg

Right, the units don't line up. Oops. Is frequency rev/sec, though? So to get from frequency to rev/min, multiply frequency by 60s/min?

But I still don't know why my velocity is off, so I can't get the right answer anyway.

4. Sep 17, 2006

### mbrmbrg

OK, got it. the problem with velocity is that WebAssign wanted 3 figures even though sig-figs only required 2.