Posted by **AP Physics B** on Sunday, September 13, 2009 at 8:42pm.

can you check my reasoning

1. The problem statement, all variables and given/known data

ok well then...

we did a lab were you have a hanging mass attached to a stirng that went through a straw and was attached to a rubber stopper. The lab was to find the mass of the rubber stopper once you know the velocity. So I was woundering if this looks correct

2. Relevant equations

f = ma

m1 = mass of stopper

m2 = mass of hanging mass

radial acceleration = r^-1 v^2

3. The attempt at a solution

net force radial = m (acceleration radial) = force of gravity on mass m2

net force radial = (m1 + m2) (acceleration radial) = m2 g

net force radial = m1(acceleration radial) + m2 (acceleration radial) = m2 g

net force radial = m1(acceleration radial) = m2 g - m2 (acceleration radial)

divided both sides by acceleration radial

m1 = (acceleration radial)^-1 ( m2 g - m2 (acceleration radial) )

at which point I plugged in the value I found for the radius

the value I found for the period

and found the radial acceleration

- AP Physics B -
**bobpursley**, Sunday, September 13, 2009 at 8:47pm
Not if I understand what you did. a mass m1 was spun horizontally, and tied to a hanging mass m2. IF that is true, then

radial force=hanging force

m2 v^2/r=m1g

I dont understand what you did.

- AP Physics B -
**AP Physics B**, Sunday, September 13, 2009 at 8:53pm
why would the hanging mass of a radial acceleration if it\'s just in equilibrium...???

m1 V^2/r = m2 g

- AP Physics B -
**AP Physics B**, Sunday, September 13, 2009 at 8:56pm
I did this

net force = (m1 + m2) (radial acceleration of mass m1) = force of gravity on mass m2

- AP Physics B -
**bobpursley**, Sunday, September 13, 2009 at 8:59pm
What was the experiment setup? Was m1 rotating horizontally? Was m2 a hanging mass attacahed to the cord holding the rotating mass?

- AP Physics B -
**AP Physics B**, Sunday, September 13, 2009 at 9:05pm
mass m1 was a robber stooper

m1 was attached to a string that went through a straw

on the other end of the straw the string came out and was attached to a mass m2

students spun mass m1 with hand on straw as the stopper spun around mass m2 the hanging mass was in equilibrium as mass m1 the stopper spun around in a circle and experienced a radial force

- AP Physics B -
**bobpursley**, Sunday, September 13, 2009 at 9:42pm
Then m2 was as I thought, it was supplying the tension counter centripetal force.

m2*g=m1*v^2/r

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