# I have to find the speed that the end of the arm goes. Can anyone

1. May 8, 2010

### poopforfood

I have to find the speed that the end of the arm goes. Can anyone help i attached a diagram

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2. May 8, 2010

### tiny-tim

Hi poopforfood!

I don't understand

all the diagram shows is a rod pivoted about its centre, and a spring which has one end fixed, and the other end attached perpendicularly to one end of the bar …

what is the rest of the question?

3. May 8, 2010

### minger

Re: Lever

I suppose that given a certain lower end position, x, you could calculate the force on the bar by the spring using Hooke's law. This force can then be used to calculate the moment, and given mass properties of the bar, instantaneous acceleration of the bar. Integrating could give you velocity as a function of time.

...I think.

4. May 8, 2010

### poopforfood

Re: Lever

sorry So I have a spring being extended at the top with a force of 51765 lbf being applied to the arm. The arm weighs approximately 2.1 lbs and is 3 feet long. The pivot point is 1 foot from the top and 2 feet at the bottom. Can anyone help me find the final velocity at the bottom point in the arm

5. May 9, 2010

### tiny-tim

Hi poopforfood!

(just got up :zzz: …)
ahh! ok, then this is a conservation of energy question …

find the potential energy of the spring at the start (when the kinetic energy is zero), and then find what the angular velocity must be when the PE is zero and it's all KE (from which you can get the velocity at the bottom).

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