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in a counter balanced system, do I need to account for both the load mass and the counter balance mass for acceleration? Answered

I have a simple 2 pulley system lifting a 2400lb mass.  Imagine a chain lift, starting at the load mass, up over a sprocket, across to a second sprocket, then down to a 3000lb counter balance mass.

to move the load down, I'll need to apply 600+ lbf down on the load.  To move the load up, I'll apply <600lbf to the load.  That's simple.  Now, during the move I need to STOP quickly.  Do I need to account for only the 600lbs difference or the 5400lbs of moving mass?

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|O                                O|
|                                      |
|                                      |
3000lb                         2400lb

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4 Replies

Burf (author)2012-02-03

I am loath to do your homework for you, but I'll give you a hint; this is a simple physics problem but you are missing one element to the equation. To solve your problem, solve this: F=ma.
Don't forget what is going on with the weights at each end of the rope as it moves.

JFunsch (author)2012-02-03

Homework I wish; scatter brained today would better response; but you have answered for me and honestly that is where I was leaning but couldn't prove it to myself that it was needed. But you are right; the Force = Mass x Acceleration (or change of velocity). In a steady state velocity, force applied would only be to move at a constant speed. In my question I gave the example to STOP quickly thus meaning there would be a quick change in velocity (or acceleration from velocity to zero). F=MA. Very good and thank you.

Burf (author)2012-02-03

Sorry about that. There are a lot of students who drop in to get their homework problems solved for them and I just assumed. Anyway, I'm glad I was able to be of help.

JFunsch (author)2012-02-03

:) understood. no worries; thanks again.