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JAMB Physics 2019 Paper

Question : 85

Total: 100

^3

, calculate the pressure it exerts on the surface.

Solution:

Concept:

Pressure is the weight of the block divided by the contact area.

For a block resting flat, this simplifies to

P = \rho g h

Explanation:

The block lies on the horizontal surface with its height vertical.

Height

h = 2\,\text{cm} = 2 \times 10^{-2}\,\text{m}

The volume is

V = \text{length} \times \text{breadth} \times \text{height} = A \times h

Mass

m = \rho V = \rho A h

Weight

W = mg = \rho A h g

Pressure

P = \frac{W}{A} = \frac{\rho A h g}{A} = \rho g h

Using

\rho = 100\,\text{kg/m}^3

g = 10\,\text{m/s}^2

, and

h = 2 \times 10^{-2}\,\text{m}

P = 100 \times 10 \times 2 \times 10^{-2}

P = 20\,\text{N/m}^2

Answer:

20\,\text{N/m}^2

So the correct option is A. $20\,\text{N/m}^2$ .

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