Ratio of Lengths b/a for Torques Equilibrium

[gcombina]

Homework Statement

A 3.0-kg ball and a 1.0-kg ball are placed at opposite ends of a massless beam so that the system is in equilibrium as shown. Note: The drawing is not drawn to scale. What is the ratio of the lengths, b/a?

(a) 2.0 (c) 3.0 (e) 5.0

(b) 2.5 (d) 4.0

Homework Equations

The Attempt at a Solution

so I did the Σtorques = 0 since the whole system is in equilibrium

Torque = Fl

1st Torque is
(mg_a)(level arm of a)

2nd Torque is

mg_b(level arm of b)

3rd Torque is
I don't know

 

[SteamKing]

No figure was attached.

Why do you think that three torques are involved in this problem?

 

[haruspex]

When calculating torques you need to keep track of which sense applies to each. Usual is to pick one sense, anticlockwise say, as positive, then any clockwise torque will be negative. (There must be some of each for the total to be zero!)