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January 29, 2015

January 29, 2015

Posted by **Cooper-Nichol** on Sunday, September 30, 2007 at 10:35pm.

a= gtan?

- Physics Derivation URGENT!! -
**Cooper-Nichol**, Sunday, September 30, 2007 at 10:51pmthat should be a= gtan? (theta, not ?)

- Physics Derivation URGENT!! -
**drwls**, Sunday, September 30, 2007 at 11:28pmWhat is the physical situation that this formula is supposed to apply to? What is theta? One can't derive a formula of this type without knowing the problem

- Physics Derivation URGENT!! -
**Cooper-Nichol**, Sunday, September 30, 2007 at 11:35pmThats my thoughts exaclty! It is this rubber stopper of mass m is in a car and then when the car accelerates it makes an angle with the veritcal which is theta. We are supposed to find a=gtantheta in terms of mass and L, which must be radius, cause the rubber stopper (which is on a string on a rear view mirror) is spinning, so something to do with centripetal motion...this is all I can gather...please try and help me with this, I know its a lot to ask, but Im drowning with this, its the only question I cant even begin to guess!

- Physics Derivation URGENT!! -
**drwls**, Sunday, September 30, 2007 at 11:42pmForget about the rubber stopper spinning and that it has a radius. Just treat it as a mass at the end of a string. The string exerts a tension force T on the stopper. When the car accelerates, the string deviates from a vertical line by an agle theta. Write down the force balance on the stopper.

T cos theta = m a

T sin theta = m g

Divide the first equation by the second:

(sin theta)/(cos theta) = tan theta

= a/g

Note that the mass cancels out.

- Physics Derivation URGENT!! -
**Cooper-Nichol**, Sunday, September 30, 2007 at 11:59pmI get it, but I think it needs to be T cos theta=mg and T sin theta =ma and then when you divide you divide Tsintheta=ma/T cos theta=mg

which leaves u with Sintetha=a/Cos theta=g

so Tantheta=a/g and then rearrange to get a=gtantheta... so thanks! a lot! This makes sense now!

- Physics Derivation URGENT!! -

- Physics Derivation URGENT!! -
- Physics Derivation URGENT!! -
**drwls**, Monday, October 1, 2007 at 2:24amYou are right; I got my sines and cosines mixed up, and then I mixed up the equaitons to cancel out my mistake. I was in too big a hurry. Nice work catching my error(s)!

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