Need some physics help

[dkgojackets]

Find T1 and T2 using m1, m2, and g. The total acceleration is g/2 downward.

Im not good with this type of stuff, but hopefully after seeing how to do this one I can figure out the more complex tension problems.

http://i12.photobucket.com/albums/a219/dkgojackets/phys.jpg

[Chips_]

Choosing the downward direction as positive.

For the mass m1

F(m1) = m1a = m1 (g/2) = + m1g + T2 - T1

youre setting the net force on m1 equal to all the individual forces on m1 which are: the force of gravity (always m1g) , T2 (going in the same direction as the acceleration for m1 so its positive) and T1 pulling in the opposite direction on m1 so it has to be subtracted.

For the second mass

F(m2) = m2(g/2) = m2g - T2

Here T2 is negative since it pulls up on mass #2. Now you can re-write the equation for T2 as

T2 = m2(g/2) substitute that in the first equation and get T1 = (m1+m2)(g/2)

In solving tension problems you always want to draw a force diagram around a point. Draw out all the forces acting on that point and set the net force equal to all the individual forces acting on it. The choice of the point depends on the problem. Sometimes its best to choose a mass and sometimes a good choice is where ropes join if you have tensions in different directions - pick a spot where the tensions meet.