Explain the meaning of centre of gravity.
Define what is meant by moment of a force.
A student is being weighed. As shown in Fig. 3.1, the student, whose weight is $W$, stands $0.30\,\text{m}$ from end $A$ of a uniform plank $AB$. The plank has a weight of $80\,\text{N}$ and a length of $2.0\,\text{m}$. A pivot $P$ supports the plank and is positioned $0.50\,\text{m}$ from end $A$. A weight of $70\,\text{N}$ is shifted to make the student’s weight balance. The plank is in equilibrium when the weight is $0.20\,\text{m}$ from end $B$.
State the two conditions required for the plank to be in equilibrium.
Determine the student’s weight $W$.
If only the $70\,\text{N}$ weight is moved, there is a maximum student weight that can be found from the arrangement shown in Fig. 3.1. State and explain one change that could be made to increase this maximum weight.