How Does a Scale Determine the Mass of a Student on a Beam?

[brentwoodbc]

A student stands on a uniform 25 kg beam.
The scale on the right reads 350 N. What is the mass of the student?

Answer is 58Kg.

I don't understand what is the deal with the scale? I think I figured this out but I'm not sure.
The force of the scale is opposite the force of the beam, girl right? If so why?
Isn't the force on the centre of rotation equal to the force on the scale?

 

[Redbelly98]

A student stands on a uniform 25 kg beam.
The scale on the right reads 350 N. What is the mass of the student?

Answer is 58Kg.

I don't understand what is the deal with the scale? I think I figured this out but I'm not sure.
The force of the scale is opposite the force of the beam, girl right? If so why?

Well, the force of the beam on the scale is opposite the force of the scale on the beam (Newton's 3rd Law), if that's what you are asking about.

Isn't the force on the centre of rotation equal to the force on the scale?

Not necessarily. That would be true only if the weight were distributed evenly between the centre of rotation and the scale.

A good approach here would be to identify all forces acting on the beam. Then:

• Balance all the forces
• Balance all the torques

The force due to the balance is simply the 350 N reading.