Work Energy Theorem and Uniform Disc Problem

theBEAST · Dec 7, 2012

Homework Statement

Using work energy theorem, solve:

Diagram of a uniform disk of mass 20 kg at the end of a strut pivoted at the floor, angled 60 degrees from horizontal, with the disk against a vertical wall; labels include m=20 kg, omega=60 rad/s, mu=0.3, r=150 mm, theta=60 degrees, g=10 m/s^2, and an angle of 30 degrees.

The Attempt at a Solution

The actual answer (3.11s) is exactly half of my answer. Does anyone know what I did wrong?

Handwritten notes on lined paper: a free-body diagram of a disc on an incline with force equations for Fx and Fy, followed by work-energy and kinematics equations solving for theta = 186.59 rad and t = 6.225.

grzz · Dec 7, 2012

Note that moment of inertia of a uniform disc about an axis through its centre and perpendicular to its plane is

[itex]\frac{1}{2}[/itex]MR[itex]^{2}[/itex].

theBEAST · Dec 7, 2012

grzz said:

Note that moment of inertia of a uniform disc about an axis through its centre and perpendicular to its plane is

[itex]\frac{1}{2}[/itex]MR[itex]^{2}[/itex].

Yup! That is what I used I believe.

haruspex · Dec 7, 2012

theBEAST said:

Yup! That is what I used I believe.

There should be two factors of 1/2 - one from Iω²/2 for the KE and another from I=Mr²/2.

Work Energy Theorem and Uniform Disc Problem

Homework Statement

The Attempt at a Solution

Discussion

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