Centripetal force on lettuce in a spinning salad spinner

[benji]

This is talking about one of those kitchen gadgets where you put the lettuce in the container and spin it so all of the water gets spun off.

The radius of the container is 12cm (0.012m). When the culinder is rotating at 2.0 revolutions per second, what is the magnitude of the centripetal force at the outer wall?

 

[ponjavic]

What have you done so far?

 

[Doc Al]

I assume they want the magnitude of the centripetal acceleration. So, what's the formula for centripetal acceleration? (Check the book!)

 

[benji]

All I've done so far is looked at equations and wrote down what I know:

Equations:
Fc=m(Ac)
Ac=(v^2)/r

What I know:
r=0.012m
rps=2.0
Fc=?

 

[Vector Sum]

Well you have rev/sec. How much distance will an object go in one rev? When you figure that out, you can find the "tangential" speed in m/s, and then your formula might make more sense.

 

[dave1234]

hey, 12cm is 0.12m.

acc= (v*v0) / r

cirumfrance = pi * 2 * 0.12 = 0.24pi

so v = (0.24pi * 2)/1 = 0.48pi

acc = 0.48pi / 0.12 = 4pi m/s*s

i think!

 

[Doc Al]

All I've done so far is looked at equations and wrote down what I know:

Equations:
Fc=m(Ac)
Ac=(v^2)/r

That's the equation you want. To use it you have to figure out the speed.

What I know:
r=0.012m

Careful. 12 cm = 0.12 m, not 0.012 m.

rps=2.0
Fc=?

Now figure out the speed using v = distance/time. It goes 2 revolutions per second. Each revolution is the circumference of a circle: $c = 2 \pi r$. Figure out the speed in m/s.

Forget the centripetal force (since you are not given a mass); you want to find the centripetal acceleration.

 

[benji]

Thanks guys, this helped a lot.