# Pendulum beam Problem

## Homework Statement

On the construction site for a new skyscraper, a uniform beam of steel is suspended from one end. If the beam swings back and forth with a period of 1.10 s, what is its length?

## Homework Equations

T=2*pi*sqroor (L/g)

## The Attempt at a Solution

(1.1/(2*3.14))^2*9.81=L

L=.3007m

This is wrong however and I don't understand why.

## Answers and Replies

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PhanthomJay
Science Advisor
Homework Helper
Gold Member

## Homework Statement

On the construction site for a new skyscraper, a uniform beam of steel is suspended from one end. If the beam swings back and forth with a period of 1.10 s, what is its length?

## Homework Equations

T=2*pi*sqroor (L/g)

## The Attempt at a Solution

(1.1/(2*3.14))^2*9.81=L

L=.3007m

This is wrong however and I don't understand why.
The period equation you have written is for a simple pendulum with a point mass at the end. You cannot use it for this case, since the mass is uniformly distributed along the beam. You must find or derive the correct formula for this case.

This is the case of physical pendulum. The gravitational force acts at centre of mass and u can assume a point mass hanging there and then calculate.

mjsd
Homework Helper
no, you will need the moment of inertia of the steel rod as well
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