(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

suppose an object A is placed on a horizontal frictionless table, and connected with a light inextensible string with a light, fixed pulley at the edge, and object B is only pulled by the vertical string that connected to a pulley.

I tried to set the acceleration up and right to be positive,

then two equations:

[tex]T-m_{A}a=0[/tex]

[tex]T-m_{B}g=m_{B}a[/tex]

so the acceleration of the system is

[tex]a=\frac{m_{B}g}{m_{A}-m{B}}[/tex]

however if I set the acceleration down (and right) to be positive, then

[tex]T-m_{A}a=0[/tex]

[tex]m_{B}g-T=m_{B}a[/tex]

the acceleration becomes

[tex]a=\frac{m_{B}g}{m_{A}+m{B}}[/tex]

they are not off by a minus sign. I can't think of a satisfactory explanation for this, and which one is correct? thanks for any help!

**Physics Forums | Science Articles, Homework Help, Discussion**

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Homework Help: Sign of acceleration in the pulley-type question

**Physics Forums | Science Articles, Homework Help, Discussion**