Question

Pulley question, why does sign of Tension and m*g change in the diagram http://prntscr.com/7bk4a2

Answer 1

in both cases Tension points up

m1*g points down
m2*g points down

Answer 2

@Michele_Laino @IrishBoy123

Answer 3

In one equation, they've considered upwards as positive and in the other one, they've considered upwards as negative.

In either case, they've selected the direction of acceleration as the positive one.

Answer 4

hmm, i thought you can't change the direction of a force arbitrarily .

Answer 5

i mean once you set one coordinate frame

Answer 6

They're two different equations. And they've set two different sign-conventions for each of them. As long as you're following the convention within an equation, it is legal.

Answer 7

You can set the same sign-convention for both equations, but you'd still get the same thing.

Answer 8

if you set the same sign convention for both equations, it would be different

Answer 9

It would remain the same.

Answer 10

Fnet = T - M1g
Fnet = T - m2g

Answer 11

In one equation, the acceleration is positive, while in the other, it is negative.

Answer 12

ok if i changed the problem a bit, using a horizontal instead of two vertical, you would use the same logic.