How Fast Does the Center of Mass of a Falling Stick Move?

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SUMMARY

The discussion focuses on calculating the speed of the center of mass of a falling stick using two methods: force and energy. Participants utilized Newton's laws, torque equations, and energy conservation principles to derive the equations governing the motion. Key equations include \( a_{cm} = -\frac{L}{2}[\ddot{\theta}\sin\theta + (\dot{\theta}^2)\cos\theta] \) and \( \omega^2 = \frac{12g(1-\cos\theta)}{L(3\sin^2\theta+1)} \). The final expression for the center of mass velocity is \( v_{cm} = -\sqrt{\frac{3gL(1-\cos\theta)(\sin^2\theta)}{(3\sin^2\theta+1)}} \).

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  • #31
Tanya Sharma said:
So, $$ ω^2 = \frac{12g(1-cosθ)}{L(3sin^2θ+1)} $$ looks alright to you ?

I like it :smile:

Tanya Sharma said:
And then

$$ v_{cm} = -\frac{L}{2}(\dotθsinθ) $$

gives $$ ω = -[\frac{3gL(1-cosθ)(sinθ)}{(3sin^2θ+1)}]^\frac{1}{2} $$

Is this fine ?
why minus? And you miss a factor of 2. $$ ω =2\sqrt{ \frac{3g(1-cosθ)}{L(3sin^2θ+1)} }$$

and Vcm=-ωsinθ L/2.
 
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  • #32
Oh ! that was a typo..I meant

$$ v_{cm} = -[\frac{3gL(1-cosθ)(sinθ)}{(3sin^2θ+1)}]^\frac{1}{2} $$

Minus makes perfect sense...
 
  • #33
Tanya Sharma said:
Oh ! that was a typo..I meant

$$ v_{cm} = -[\frac{3gL(1-cosθ)(sinθ)}{(3sin^2θ+1)}]^\frac{1}{2} $$

Minus makes perfect sense...

$$ v_{cm} = -[\frac{3gL(1-cosθ)(sin^2θ)}{(3sin^2θ+1)}]^\frac{1}{2} $$
sinθ has to be squared if you pull it under the square root. But otherwise it is perfect:thumbs: Have a good rest, you deserve it. :smile:

ehild
 
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  • #34
ehild...I am falling short of words to express my gratitude...All I will say is "THANK YOU ehild" .

You rock! :smile:
 
  • #35
Tanya Sharma said:
ehild...I am falling short of words to express my gratitude...All I will say is "THANK YOU ehild" .

You rock! :smile:

You are welcome. That was a challenging problem. I am also exhausted :smile:

ehild
 

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