Can you please help me with Newtons 3rd Law


by slobodan48
Tags: newtons third law, physics, quiz, test
slobodan48
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#1
Dec2-09, 03:57 PM
P: 9
how do you find the Tension force,acceleration,magnitude.
Its those questions where you have pullys,boxes pushing each other...
I am really confused for the 3rd law
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Cryxic
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#2
Dec2-09, 05:34 PM
P: 53
Quote Quote by slobodan48 View Post
how do you find the Tension force,acceleration,magnitude.
Its those questions where you have pullys,boxes pushing each other...
I am really confused for the 3rd law
Do you have a specific example? I'd hate to just vapidly repeat the definition of the 3rd law, which you can easily find anywhere and everywhere....
slobodan48
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#3
Dec2-09, 06:05 PM
P: 9
Two masses are places in a frictionless pulley system.Solve for the acceleration and tension forces.
1st box is 4kg and the other is 3kg

well i know,
fnet=ma
fg=mg
ff=muFn

sophiecentaur
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#4
Dec3-09, 10:40 AM
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Can you please help me with Newtons 3rd Law


You could start by saying that there is a net, unbalanced force of 10N (For GCSE level thought - or you can do 9.81m/s/s, if you like), pulling one up and one down.
This is accelerating both the masses (7kg total), use your formula to find the acceleration.
The tension will be ml times (g + this acceleration) for the light mass and also mh times (g- this acceleration) for the heavy mass. Those two values should be the same, natch - as a check.
etc etc - you can put in the numbers


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