So to find the mass we must use the formula D=M/V but because we don’t have the mass, we must use the formula M=DxV
So to find volume, just multiple the length (0.4m) width (0.4m) and height (2m) and you will get 0.32m as the volume. Now multiple this volume with your given density of 2,400 kg/m and you will get 768 kg as the mass of the marble block.
Final answer: 768 kilograms (kg) as mass of the marble block.
It is A: They add energy to the work
I believe the answer is C, 3
Answer:

Explanation:
Given that,
Mass of a brick, m = 3.1 kg
The dimensions of the brick 225 m x 112 m x 75 m
We need to find the maximum pressure created by the brick. We know that, the force acting per unit area is called pressure exerted. It is given by the formula as follows :

F = mg
A = area with minimum dimensions i.e. 112 m x 75 m
Pressure is maximum when the area is least.
So,

So, the maximum pressure created by brick is
.
Geologists use the Mohs Harness Scale (aka the Scratch Test) to determine the hardness of a mineral.
For more info, check out http://geology.com/minerals/mohs-hardness-scale.shtml