Find Angular Acceleration: Torque & Rotational I

AI Thread Summary
The discussion revolves around calculating angular acceleration for a system involving two masses on a rigid rod. The center of mass is determined to be located 2/3 L below the top mass. The participant struggles with applying the torque formula, specifically how to compute the moment of inertia (I) correctly. There is confusion about the relationship between torque, radius, and force, particularly in determining the effective radius for torque calculations. Clarification is sought on the correct approach to finding torque and its relation to angular acceleration.
wushumaster
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Homework Statement


The figure shows a view from above of two objects attached to the end of a rigid massless rod at rest on a frictionless table. Imagine a vertical rod, on the top end is a mass of m, an the bottom is a mass of 2m. The length of the rod is L and L/4 down from m (at top), a horizontal and rightward force is applied. When this F is applied, the resulting rotational acceleration of the rod about its center of mass is kF/(mL).

Homework Equations


What is K?

The Attempt at a Solution


So I found the center of mass as 2/3 L below mass m. but I don't understand how we can get torque (like I know its r cross F), but.. We can use torque=I times angular acceleration. But i got I wrong. HELP! please!
 
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oh! is it just because torque equals r cross f and that means it equals 2/3 L- 1/4 L?
 

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