2 weights on a pully, show formula

  • #1

Homework Statement



The apparatus (see link to image) is used to measure the free fall acceleration g by measuring the acceleration of the two blocks connected by a string over a pulley. Asume a massless, frictionless pulley and a massless string.
http://img3.imageshack.us/img3/3459/phys.th.png [Broken]
a) draw a free body diagram of each block
http://img16.imageshack.us/img16/3523/diagrams.th.png [Broken]
b)use the free body diagrams and Newton's laws to show that the magnitude of acceleration of either block and tension in string are a=(m1-2)/(m1+2)
c)do these expressions give reasonable results if m1=m2 in the limit that m1 >> m2 and in the limit that m1 << m2 ? Explain

Homework Equations



Fnet=ma
Fg=mg


The Attempt at a Solution


F=ma
T_1=-T_2
T_2=(m_2)g
T_1=(m_1)g
=>m_1(g)=-m_2(g)
 
Last edited by a moderator:

Answers and Replies

  • #2
rock.freak667
Homework Helper
6,230
31
Assume block one moves downwards, so the resultant force on m1 is

m1a=mg-T

So what is the resultant force on m2?

Now you have two equations in T and a, you can now eliminate T.
 

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