A uniform bar weighing 40N and measuring 2cm is hinged at one end so that the unhinged end can move up and down. If it is held horizontally by a spring balance at 0.3m from the free, determine the reading of the spring balance

First, let's calculate the torque caused by the weight at the given distance from the hinged end of the bar.

Torque = Force x Distance
Torque = 40 N * 0.2 m
Torque = 8 Nm

Now we need to find how much force the spring balance is applying in order to keep the bar in equilibrium state. This is given by the equation:

Force = Torque / Distance
Force = 8 Nm / 0.3 m
Force = 26.67 N

So the reading of the spring balance is 26.67 N.