Note: Density is often measured in grams per centimetre cubed (g cm3) as this can be convenient for many laboratory experiments. In order to convert from g cm3 to kg m3 we multiply by 1 000.
SAMPLE PROBLEM 4D Mercury has a density of 13.6 g cm3. What is its density in SI units?
SAMPLE ANSWER 4D Q
Q ‹
‹ 3 13.6 103 kg m3
1 m3 1 000 000 cm3 13.6 g cm3 1 cm3 has a mass of 13.6 grams 1 000 000 cm3 has a mass of 13.6 106 grams 1 m3 has a mass of 13.6 103 kilograms 13.6 g cm3
EXERCISE 4.2 DENSITY
Q1 Calculate the mass of a cube of sides 1.5 m in length, given that it’s made from a material of density 85 kg m3. Q2 Calculate the mass of water in a swimming pool of length 50 m, width 20 m and depth 1.8 m, given that the density of water is 1 103 kg m3.
Q3 Calculate the density of a body of mass 52 g and volume 65 cm3. Give your answer in SI units. Pressure
PRESSURE Pressure (P or p) is force per unit area.
It is a scalar quantity with an SI unit of pascal (Pa). Pressure acts in all directions; this is equivalent to saying it has no direction.
1 pascal is the amount of pressure when 1 newton of force is applied over an area of 1 metre squared.
1 Pa 1 N m2 Note: The SI unit of area is metre squared (m2).
SAMPLE PROBLEM 4E
A solid block in the shape of a cube with sides of length 120 cm rests on a table.The weight of the block is 720 N. Calculate the pressure it exerts at the table.
