(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

A thin steel beam 8.0 meters long is suspended from a crane and is undergoing torsional osciallations. Two 75-kg steelworkers leap onto opposite ends of the beam, as shown in the figure (no figure given, they just jump straight towards the center of the beam).

If the frequency of the oscillations diminishes by 20%, what is the mass of the beam?

2. Relevant equations

Iw_1 = Iw_2 + 2 (m R^2 w_2)

I = (1/12) ML^2

w = 2 (pi) (freq.)

3. The attempt at a solution

I (w_1) = I (w_2) + 2 (m R^2 w_2)

I (w_1) = (w_2) (I + 2 (m R^2))

I (w_1) = ((80%) w_1) (I + 2 (m R^2))

I = (80%) (I + 2 (m R^2))

I = 80% I + 80% 2 (m R^2)

(2/10) I = (8/10) 2 (m R^2)

I = 8 (m R^2)

I = 8 (75 R^2)

I = 600 R^2

But I = (1/12) ML^2, so:

600 R^2 = (1/12) ML^2

M = 7200 R^2 / L^2

M = 7200 (4^2) / (8^2)

M = 1800

Mastering physics does not accept this answer. What is wrong with my solution?

**Physics Forums | Science Articles, Homework Help, Discussion**

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Homework Help: Torsional Oscillations Question

**Physics Forums | Science Articles, Homework Help, Discussion**