Question

Fig. 3.18 below shows a wheel barrow of mass $15kg$ carrying a load of $30kgf$ with its centre of gravity at A. The points B and C are the centre of wheel and tip of the handle such that the horizontal distance $AB=20cm$ and $AC=40cm$.
Find:
(a) the load arm,
(b) the effort arm,
(c) the mechanical advantage, and
(d) the minimum effort required to keep the leg just off the ground

Answer 1

For the equilibrium the torque has to be balanced about the wheel

$\begin{array}{c}Weight\times BA=Force\times BC\\ Force=\frac{W\times BA}{BC}\\ F=\frac{300\times 20}{60}\\ F=100N\end{array}$

So, when the applied force is slightly more than $100N$ the wheel barrow will lift off the ground.