# Rotational Energy in Bat Contraption

#### tiredphysicsstudent

I missed this one question on my Physics Free Response Test and I need help figuring out what the answer is because man Im completely lost. So the question is that a student sets up an experiment to determine the rotational inertia of the bat where a light rod that is .9 m long is attached to the handle of the bat and the other end is connected to a frictionless axis and this system is held horizontally. Its allowed to rotate through the vertical position.

So what measurements (and how) do I need to get to calculate the rotational inertia and how can I use these measurements to find the rotational inertia

#### Cervesa

What lab measuring equipment is available? Is the mass of the bat known and has the center of mass for the bat been located?

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#### tiredphysicsstudent

anything commonly found in a physics classroom can be used and the center of mass has not been found
What lab measuring equipment is available? Is the mass of the bat known and has the center of mass for the bat been located?

#### tiredphysicsstudent

and the mass is not known

#### Cervesa

The first measurement you need is the bat’s mass. Should be able to find that with a spring scale.
You can also determine the COM via rotational equilibrium by hanging the bat horizontally by a support at one end and a spring scale at the other.

I assume this is a fairly modern HS physics lab and a photogate is available. Ever use one?
The photogate is able to measure linear speed when a thin cardboard “strip” of known width passes through it.
The strip’s mass is negligible and can be attached to a position on the bat such that it passes through the gate at the bottom of its swing.

Finally, I’ll tell you that conservation of energy is probably the easiest way to determine the bat’s rotational inertia.

$mgh = \dfrac{1}{2}I \omega^2$

#### tiredphysicsstudent

Yes, I love photogates, what a nifty tool.
And yea that makes sense tysm
The first measurement you need is the bat’s mass. Should be able to find that with a spring scale.
You can also determine the COM via rotational equilibrium by hanging the bat horizontally by a support at one end and a spring scale at the other.

I assume this is a fairly modern HS physics lab and a photogate is available. Ever use one?
The photogate is able to measure linear speed when a thin cardboard “strip” of known width passes through it.
The strip’s mass is negligible and can be attached to a position on the bat such that it passes through the gate at the bottom of its swing.

Finally, I’ll tell you that conservation of energy is probably the easiest way to determine the bat’s rotational inertia.

$mgh = \dfrac{1}{2}I \omega^2$