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Torque and forces.

  • Thread starter mathildej
  • Start date
1
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1. Homework Statement
Two balls are connected together and fall through air. They also rotate around the center of mass. I'm supposed to find an equation for the torque of air resistance through the center of mass.
Fk= Force due to air resistance on each of the balls
w=angular velocity
Vcm=velocity of the center of mass
M=mass of each ball
R=radius of each ball
Kv=constant
T=torque
Icm=moment of inertia in the center of the mass
Ia=Ib= moment of inertia for each ball
r= position of the ball relative to the center of mass

2. Homework Equations
Ia=Ib=(2/5)MR^2
Fk=-2Kv*Vcm
Icm=(14/5)M(R^2)
Va=Vcm+w X r
Vb=Vcm - w X r
This is the answer I'm supposed to get: T=-2Kv*w*R^2

3. The Attempt at a Solution
I have tried sooo many different ways to get this.
And still I have no idea. Can anyone help me?
 

Answers and Replies

Hootenanny
Staff Emeritus
Science Advisor
Gold Member
9,598
6
I have tried sooo many different ways to get this.
And still I have no idea. Can anyone help me?
Hi mathildej and welcome to PF,

Would you mind detailing some of the methods you have tried?
 

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