Question

A rectangular wooden block has mass of 4 kg. The length, breadth and height of this wooden block are 50 cm, 25 cm and 10 cm, respectively. Find the pressure on the table top:

(a) When the wooden block is kept with its surface measuring $50cm\times 25cm$ on the table.

(b) When the wooden block is kept with its surface measuring $25cm\times 10cm$ on the table.

(Assume: Acceleration due to gravity, $g=10m{s}^{-2}$) [5 MARKS]

Answer 1

Each problem: 2.5 Mark

Given, mass of wooden block, m = 4 kg,
acceleration due to gravity, $g=10m{s}^{-2}$
We know, weight of wooden block, $W=m\times g$
$\Rightarrow W=4\times 10$
$\Rightarrow W=40N$
Since, weight is a force, so we can say that the force exerted by the wooden block on the table top is 40 N. We will now calculate the pressure in the two cases.

(a) In the first case: Force = 40 N
and, $area=50cm\times 25cm$
$=\frac{50}{100}m\times \frac{25}{100}m$
$=0.5m\times 0.25m$
$=0.125m^2$
Now, $Pressure=\frac{Force}{Area}$
$=\frac{40}{0.125}$
$=320N{m}^{-2}$
Thus, the pressure exerted by the wooden block on table top when kept on its face measuring $50cm\times 25cm$ is $320N{m}^{-2}$ or 320 pascals
(b) In the second case: Force = 40 N
And, $Area=25cm\times 10cm$
$=\frac{25}{100}m\times \frac{10}{100}m$
$=0.25m\times 0.1m$
$=0.025m^2$
Now, $Pressure=\frac{Force}{Area}$
$=\frac{40}{0.025}$
$=1600N{m}^{-2}$
Thus, the pressure exerted by the wooden block on table top when kept on its face measuring $25cm\times 10cm$ is $1600N{m}^{-2}$ or 1600 pascals.