Question

In an experiment, a cement block of mass 14 kg was placed on top of 8 (carefully arranged) eggs without breaking the eggs.
1) Calculate the force per egg caused by the weight of the block.
2) If the pressure on each egg is 25 N/mm 2 , calculate the contact area, in mm 2 , between the block and one egg.

Answer 1

Answer:

1) The force per egg caused by the weight of the block is 17.15 N

2) $A= 0.686\ mm^2$

Explanation:

Pressure

The pressure is computed as the force acting upon a surface divided by the area of the surface :

$P=\frac{F}{A}$

The weight of an object of mass m is:

W = mg

Where g is the gravitational acceleration of $9.8\ m/s^2$

The cement block has a mass of m=14 kg, thus its weight is:

W = 14*9.8

W = 137.2 N

1) This weight is evenly distributed over the 8 eggs, thus the force per egg is:

F = 137.2 N/8= 17.15 N

The force per egg caused by the weight of the block is 17.15 N

2) It's given the pressure on each egg as $P= 25 \ N/mm^2$ and we know the force acting on each one is F=17.15 N. To find the contact area we solve the formula of the pressure for A:

$\displaystyle A=\frac{F}{P}$

$\displaystyle A=\frac{17.15}{25}$

$\mathbf{A= 0.686\ mm^2}$