How to calculate weight of object swinging a radius?

[dishguy55]

Homework Statement

20 lbs. on the end of a 30 inch arm. Dropping from 2oclock position to 5oclock position.

How much wieght will be developed if this was dropped on a scale measuring lbs.

Homework Equations

I am unsure how to calculate this.

The Attempt at a Solution

If there is a formula I can try to calculate myself.
I just don't know where to start.

 

[danielakkerma]

Hi there...
Let me see if I get this straight:, by

...if this was dropped on a scale measuring lbs.

did you mean that at that juncture, on this sort of pendulum, the thread/rope(whatever) is suddenly cut, and the object is dropped on a weight measure?
If that's the case, then you must consider what sort of forces act upon an object moving in such a structure; Essentially(and this is quite a hint), you need to think about circular motion...
Give it a try, it's bound to work...
Good luck,
Daniel

 

[dishguy55]

Ok. i researched that and found this formula.

w=2*3.14/t.

w in my angular velocity. that is what i need to know.

t is the period for 1 rotation.

Is the rotation in rpm.

I know my rpm is 19.

If so then w would be .33

If my angular velocity is .33

How does that convert to lbs?

 

[danielakkerma]

Well, let me simply rearrange what you wrote, if you don't mind...
You're correct in positing that: $$\omega = \frac{2\pi}{t}$$, Where t is the time of a single rotation(however, in SI units, this is ALWAYS measured in seconds); Therefore, RPMs won't do.
My advice is(based on my personal experience) is to try and convert any problem to metric units(SI based), and if the solution explicitly requires Imperial/non-standard representation, only then(after having the proper resolution), should you turn it back to whatever's necessary(but that's my opinion, and you're of course free to do what you're comfortable with).
As for those pesky Lbs, think about what a force suggests, its equation, and what do Lbs represent in this case(Newton's 2nd law would be helpful).
You're on the right track though,
Daniel

 

[rwisz]

Can you provide more information about the object and its motion? Is it a pendulum swinging back and forth, or is it being dropped from a height and swinging like a pendulum? Also, is the object swinging on the same arm or is it being released from the 2 o'clock position and then caught at the 5 o'clock position by a different arm? These details will affect the calculations needed to determine the weight of the object. Generally, to calculate the weight of an object swinging on a radius, you would need to know the mass of the object, the length of the arm, and the angular velocity of the object. From there, you can use the formula F=ma to calculate the force exerted by the object on the arm, which can then be converted to weight using the formula W=mg. However, without more information, it is difficult to provide a specific answer.