How to Determine Unknown Masses in an Atwood's Machine?

[imsoconfused89]

AP PHYSICS MIDTERM-EMERGENCY!.please help

Homework Statement

We are given an Atwoods machine with two known masses on either side. On one of the masses two objects of unknown mass are added. We have to perform measurements to determine the resulting acceleration. Then from the accelerations we have to calc. the mass of each oth the unknown objects to the nearest .01 kg. we are not given the masses of the two known objects YET..so can we just call them a and b.

Homework Equations

F=ma
Fmg=9.8
mg-t=ma

The Attempt at a Solution

i have no idea of even to start it except that maybe we use mg-t=ma and go from there?
then would i consider t-mg=ma and have m(1)a(1)=m(2)a(2)
would anyone know how to do this
the link to the actual website where the ? is posted is

http://fc.pickerington.k12.oh.us/~doug_forrest/F00013CE5/S012A3894.-1/AP exam info07.pdf?WasRead=1

 

[AngeloG]

A good idea would to first start off by drawing some basic diagrams of how the forces are working and which way things are accelerating =).

But you are right that you would use ma and that tension would be involved. You just need to set it up visually to get a grasp of how things are going.

Also, be sure to set when you draw you free body force diagram or force diagram to set your + and -'s.

*Hints*
Tension basically brings all this together to make one nice equation which you can solve for acceleration. hehe =p.

 

[imsoconfused89]

well ok. that helped i think
so if we do the
(unknown mass)(9.8)=net force
(sum of two known masses)+x=mass total
a=f/m
so... 9.8x/(sum of two known masses+x)=a

then solve for x from the solved acceleration which we wouldve used
x=.5at^2

is that right?