Question

7 A brick of weight 20N and dimensions 20 cm x10cm x 5cm is placed once on its

largest surface area and then on its smallest surface area on the ground. Find out

the ratio of the pressure exerted by the brick.​

Answer 1

Answer:

1:4

Explanation:

w=mg=F=20N

20x10x5=lxbxh

P=F/A

Pl=Pressure on large surface area

Ps=Pressure on small surface area

Pl/Ps=20x10x5/20x10x20=1/4

Pl:Ps=1:4 (Ans)

Answer 2

Concept:

Pressure: The force applied per unit area is called pressure. Its S.I. unit is pascal (Pa). Mathematically it can be expressed as,

Pressure (P) = Force (F)/Area (A)

Given:

Weight of brick, w = mg = 20 N

Dimensions of brick = 20 cm × 10 cm × 5 cm

= 0.2 m × 0.1 m × 0.05 m

∴ Length of brick, l = 0.2 m

Breadth of brick, b = 0.1 m

Height of brick, h = 0.05 m

Find:

The ratio of the pressure exerted by the brick.

Solution:

Case 1: When brick is placed on its largest surface -

Force ($F_1$) = Weight (w) = 20 N

Area of the largest surface, $A_1$ = Length x Breadth

                                                 = l x b = 0.2 x 0.1 = 0.02 m²

$Pressure = \frac{Force}{Area}$

$P_1 = \frac{F_1}{A_1}$

$P_1 = \frac{20}{0.02} \\\\P_1 = 1000 Pa$

Case 2: When brick is placed on its smallest surface -

Force ($F_2$) = Weight (w) = 20 N

Area of the largest surface, $A_2$ = Height x Breadth

                                                 = h x b = 0.05 x 0.1 = 0.005 m²

$Pressure = \frac{Force}{Area}$

$P_2 = \frac{F_2}{A_2}$

$P_2 = \frac{20}{0.005} \\\\P_2 = 4000 Pa$

Ratio of pressure exerted is given by,

$\frac{P_1}{P_2} = \frac{1000}{4000}$

$\frac{P_1}{P_2} =\frac{1}{4} \\\\P_1:P_2 = 1:4$

Answer:

The ratio of pressure exerted by the brick is 1:4.

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