Question

A block of wood is kept on table top. The mass of wooden block is 5 kg and its dimensions are $40cm\times 20cm\times 10cm$. Find the pressure exerted by the wooden block on the table top, if it is made to lie on the table top with its sides of dimensions (a) $20cm\times 10cm$ and (b) $40cm\times 20cm$

• A. (a) $P=2440N{m}^{-2}$ (b) $P=610.5N{m}^{-2}$
• B. (a) $P=2450N{m}^{-2}$ (b) $P=612.5N{m}^{-2}$
• C. (a) $P=2460N{m}^{-2}$ (b) $P=618.5N{m}^{-2}$
• D. (a) $P=2470N{m}^{-2}$ (b) $P=712.5N{m}^{-2}$

Answer 1

Answer: (B)

(a) $P=2450N{m}^{-2}$ (b) $P=612.5N{m}^{-2}$

Mass of the wooden block, $m=5kg$
Thrust due to wooden block,
$Mg=5kg\times 9.8m{s}^{-2}=49N$
(a) Surface area of $20cm\times 10cm$ surface,
$A=(20\times 10)c{m}^2$
$=(0.2\times 0.1)m^2$
$=0.02m^2$
$P=\frac{mg}{A}$
$P=\frac{49N}{0.02m^2}=\frac{49}{0.02}N{m}^{-2}$
or Pressure, $P=2450N{m}^{-2}$.
(b) Surface area of $40cm\times 20cm$ surface,
$A=(40\times 20)c{m}^2$
$=(0.4\times 0.2)m^2=0.08m^2$
$P=\frac{49N}{0.08m^2}=\frac{49}{0.08}N{m}^{-2}$
or Pressure, $P=612.5N{m}^{-2}$.