In this question a misbehaving student sits
on a table that can only carry a certain amount
of weight. His weight is equal to m, his mass,
multiplied by g, the acceleration due to gravity.
This weight is spread evenly over the four
table legs. Each will bear a force F. In turn,
the table exerts a reaction force on the student
that acts vertically upwards and is of magnitude
4F. This is the sum of the four reaction forces
acting from the table legs on the table which,
in turn, exerts a force of magnitude 4F on
the student. Therefore if the student is in
equilibrium on the table the magnitude of
the two vertical forces acting on him will
be equal, so 4F = mg. We can rearrange this
to find F, the force on each table leg. The
table legs will break if this force exerted
upon them is greater than 150N. We can now
compare our expression for F to 150N to see
if the table legs will break or not.
