Chapter 10, Problem 7P

(a)

To determine

To Find: The pressure exerted on a floor by chair.

Answer to Problem 7P

The pressure exerted on a floor by one pointed chair leg is $7.35\times {10}^7\text{ Pa}$ .

Explanation of Solution

Given info:

Area, $A=0.020{\text{ cm}}^{\text{2}}\text{ = }0.020\times {10}^{-4}{\text{ m}}^{\text{2}}$

Weight exerted by chair with all four legs, $w=\left(60\text{ kg}\right)g$

Weight exerted by one leg, $Mg=\frac{mg}{4}=\frac{60g}{4}=\left(15\text{ kg}\right)g$

Formula used:

Write the expression for the pressure.

  $P\text{ = }\frac{\text{Force (}F\text{)}}{\text{Area (}A\text{)}}$

Write the expression for the force applied due to weight.

  $F=M\times g$

Calculation:

Substitute the given values in the above equation,

  $\begin{array}{c}P=\frac{M\times g}{A}\\ =\frac{15\times 9.8}{0.020\times {10}^{-4}}\\ =7.35\times {10}^7\text{ Pa}\end{array}$

Conclusion:

Thus, the pressure exerted on a floor by one pointed chair leg is $\text{7}\text{.35}\times {\text{10}}^7\text{ Pa}$ .

(b)

To determine

To Find: The pressure exerted on a floor by elephant.

Answer to Problem 7P

The pressure exerted on a floor by standing elephant is $183750\text{ Pa}$ .

Explanation of Solution

Given info:

Area, $A=800{\text{ cm}}^{\text{2}}\text{ = }800\times {10}^{-4}{\text{ m}}^{\text{2}}$

Mass of elephant, $m=1500\text{ kg}$

Formula used:

Write the expression for the pressure.

  $P\text{ = }\frac{\text{Force (}F\text{)}}{\text{Area (}A\text{)}}$

Write the expression for the force applied due to weight.

  $F=m\times g$

Calculation:

Substitute the given values in the above equation,

  $P=\frac{m\times g}{A}=\frac{1500\times 9.8}{800\times {10}^{-4}}=183750\text{ Pa}$

Conclusion:

Thus, the pressure exerted on a floor by standing elephant is $183750\text{ Pa}$ .