Question

Three boxes are stacked on top of each other. The top box weighs 5 kg, the middle 20 kg and the bottom box weighs 50 kg.
Draw out all the forces acting on the middle box
Determine the magnitude of the forces

Answer 1

Explanations & calculations

• Refer to the figure attached.
• To calculate each force, apply Newtons second law upward the each box.
• g=9.8 ms^-2

• Considering the vertical equilibrium of the top box ,

$\qquad\qquad \begin{aligned} \small R-5g &= 0\\ \small R&= \small 5g = \bold{49N} \end{aligned}$

• Considering the vertical equilibrium of the middle box,

$\qquad\qquad \begin{aligned} \small S-R -20g &= \small 0\\ \small S &= \small 49N+(20\times9.8) = \bold{245N} \end{aligned}$

• Considering the vertical equilibrium of the box at the bottom,

$\qquad\qquad \begin{aligned} \small P-S-50g &= \small 0\\ \small P &= \small 245N + (50\times9.8) =\bold{735N} \end{aligned}$