The diagram shows a girl attempting (but failing) to lift a heavy suitcase of weight $W$. The magnitude of the vertical upwards pull of the girl on the suitcase is $P$ and the magnitude of the vertical reaction of the floor on the suitcase is $R$.

Which equation correctly relates $W$, $P$ and $R$?

A.     $W = P + R$

B.     $W > P + R$

C.     $W < P + R$

D.     $W = P = R$

A

The majority of candidates selected an incorrect option, as a result of a misunderstanding of equilibrium. Candidates should have realized that during equilibrium the sum of the vertical upwards forces acting on the suitcase will be equal in magnitude to the sum of the vertical downwards forces.