Question

a block of wood is kept on a table top . the mass of wooden block is 5kg and its dimensions are 40 x 20cm x 10cm. find the pressure exerted by the wood block on the tale top if it is made to lie on the table top with is sides of (sa) 20cm x 10 cm and (b) 40cm x 20 cm

Answer 1

$$\begin{gathered} \mathbf{Gravitational}\mathbf{}\mathbf{Force}\mathbf{:} \\ {\mathrm{F}}_{\mathrm{g}}=\mathrm{mg} \\ =5\times 9.8 \\ =49\mathrm{N} \\ \mathrm{Case}\mathrm{I}: \\ \mathrm{Surface}\mathrm{area}\mathrm{of}\mathrm{contact}\mathrm{with}\mathrm{the}\mathrm{table}\mathrm{top},\mathrm{A}=20\mathrm{cm}\times 10\mathrm{cm} \\ =0.2\mathrm{m}\times 0.1\mathrm{m} \\ =0.02{\mathrm{m}}^2 \\ \mathrm{Pressure}\mathrm{exerted},\mathrm{P}=\frac{{\mathrm{F}}_{\mathrm{g}}}{\mathrm{A}} \\ =\frac{49}{0.02} \\ =2450\mathrm{Pa} \\ \mathrm{Case}\mathrm{II}: \\ \mathrm{Surface}\mathrm{area}\mathrm{of}\mathrm{contact}\mathrm{with}\mathrm{the}\mathrm{table}\mathrm{top},\mathrm{A}=40\mathrm{cm}\times 20\mathrm{cm} \\ =0.4\mathrm{m}\times 0.2\mathrm{m} \\ =0.08{\mathrm{m}}^2 \\ \mathrm{Pressure}\mathrm{exerted},\mathrm{P}=\frac{{\mathrm{F}}_{\mathrm{g}}}{\mathrm{A}} \\ =\frac{49}{0.08} \\ =612.5\mathrm{Pa} \end{gathered}$$