Moments Exemplar Question

Now let's tackle an examination question... consider the following example:  

The ruler is suspended in the centre therefore it is balanced before the balloon is added. When the balloon is added it pulls down on the right hand side with a moment of 0.06N x 16 cm and produces a turning moment of 0.96 Ncm. This will make the ruler turn in a clockwise manner.

If another balloon is added as shown below the system can be put into equilibrium - balanced so that no turning takes place. That happens because the balloon pulls upwards producing an anticlockwise moment of an equal size to the clockwise moment.

Can you work out the value of force F?

Click here for the solution.