How Do You Calculate the Torsional Constant of a Wire?

[Robertoalva]

1. A 560 g hollow ball 18 cm in diameter is suspended by a wire and is undergoing torsional oscillations at a frequency of 0.78 Hz. What is the torsional constant of the wire?

Homework Equations

F=-κθ
ω=sqrt(κ/I)

The Attempt at a Solution

tried to use the frequency to get the angular displacement and then just solve for k but I didn't get the answer

 

[Robertoalva]

do i have to use the rotational inertia of the hollow sphere? 2/3 M R^2 ??

 

[SammyS]

1. A 560 g hollow ball 18 cm in diameter is suspended by a wire and is undergoing torsional oscillations at a frequency of 0.78 Hz. What is the torsional constant of the wire?

Homework Equations

F=-κθ
ω=sqrt(κ/I)

The Attempt at a Solution

tried to use the frequency to get the angular displacement and then just solve for k but I didn't get the answer

Can you write the angular displacement of the ball as a function of time ?

do i have to use the rotational inertia of the hollow sphere? 2/3 M R^2 ??

Yes. You will need that.

 

[Robertoalva]

as time... wouldn't it be something as Acoswt ?

 

[Robertoalva]

i already solved it! thanks! it was using this k=(w^2 )(I)