So for Physics 1B03, I think the answer in the system is wrong for one of the question (and possibly then for the subsequent follow up questions) b/c I'm pretty damn sure I'm doing this correct. Problem is you have a table with two pulleys on either side, one block hanging off each side of the table and one block on the table connecting the two ropes. From left to right, m1=4.15kg, m2=1.40kg, m3=2.14kg, coefficient of kinetic friction b/w m2 and table is 0.340, pulleys are frictionless, find the magnitude of the acceleration of the blocks. The final formula I get is: a=g(m3-m2uk-m1)/(m1+m2+m3)=-3.168m/s^2 and the magnitude would just be positive. and thats the wrong answer I tried putting in 3.17, 3.168 etc. nothing happening.

Try putting in a negative answer. Sometimes that's all it takes. Frickin' CAPA.

Pro tip: sometimes, you can find explanations on the net. Just google that question and there's a high probability of it being asked. Also, good luck!

If that doesn't work, remember to draw your picture and place all directions so you get your signs right. It really helps. I'd help 'ya, but I don't want to. I took a year off of taking Physics courses for a reason.

try again


I get a different answer

You are messing up on one piece of logic (think about the middle block).

Hint: You you are doing the problem backwards.That is to say you are considering down and right positive as opposed to left and down positive which is actually where the block will go. (draw it out since m1 is heavier that blocks will move towards m1.) You can do the problem backwards but then you got to make sure the signs on all your forces is right. So again check the middle block (think it through draw force diagrams)