Angular Acceleration of a falling pole

  • #1

Homework Statement



A 7.0m -tall electrical pole with mass 260 kg has a 42 kg electrical transformer attached to its very top. The pole is hit by lightning at its base, nearly severing the pole from its base. The pole begins to fall, rotating about the part still connected to the base.

Estimate the pole's angular acceleration when it has fallen by 25 degrees from the vertical.

Homework Equations



Angular Acceleration = Net torque / Inertia
Torque = r*perpendicular force
Inertia = m1*r1^2+m2*r2^2*m3*r3^3 etc

The Attempt at a Solution



So I started out working on the Torque
T1=7*42*-9.8*sin(25)
T2= 3.5*9.8*260*sin(25)

This gave me
T1=381.3
T2 = 1180.3

Thus net torque = 381.3+1180.3 = 1561.6

Then I started on the inertia:
I = 42*7^2+(1/3)*260*7^2
I = 6304.666

So the acceleration is 1561.6/6304.666
A= 0.247 rads/s^2

This answer isn't right, but I can't figure out how I went wrong.
Any help would be greatly appreciated.
 

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