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[ILikePie]

I have a physics exam tomorrow and I'm not really sure how tension with acceleration works.
Say I have a figure like so:

Spoiler (click to show/hide)

m1 is being pulled down by m2.

If m1's mass is 5kg, and m2's mass is 10kg, the table and roller are frictionless, and the string's mass is 0 (Aren't high-school physics just wonderful?), how do I calculate the tension on the string?
I'm guessing it'd be something like this:

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g = 10n                   (Yeah, high-school)
m2*g = 100n               (force of gravity on m2)
a = 100n/5kg = 20m/s^2    (m1's acceleration, (m2*g)/m1)
T = 100 - 20 = 80         (m2*g - a)
I'm pretty sure I'm wrong somewhere, help?

[Hubris Incalculable]

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g = 10n (Yeah, high-school)


In my highschool physics class, we did 9.8m/s².

[ILikePie]

Yeah well, things get easier over the years I guess. Either that, or we Israelis are just a bit "dumb".
Anyway, Wikipedia gives this formula for a system under net force: ΣF = T - mg. In this case, what do put as ΣF, and what do I put as mg? (Aren't ΣF and mg both m2*g (100n)?)

[nogoodnames]

Since Ft1 = Ft2 and a1 = a2 you can set up the following two equations for the net force on each mass:

Fnet1 = m1*a = m1*g - Ft

Fnet2 = m2*a = Ft

rearrange to get a= Ft/m2, then substitute that into the first equation and solve for Ft. If I'm right it turns out to be about 33N.

Edit: Whoops, I put in the wrong mass numbers. The result should be the same but m1 is the hanging mass and m2 is the mass on the table.

[ILikePie]

Thanks, I get it now.