Density and Pressure
5 marks · NormalA glass block has dimensions 0.2 m × 0.10 m × 0.05 m and a mass of 2.5 kg. Calculate the density of the glass. State the correct unit.
The block is laid flat on a table. Calculate the pressure it exerts on the table. Give your answer in pascals.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
Show answer
(a) 2500 kg/m^3 · must show Correct substitution, Correct unit
(b) 500 Pa · must show Correct area chosen, Force calculated as weight
Common mistakes: Using wrong area for pressure; Wrong units for density
Show mark scheme and worked solution
Marking points
M1 (a) · 1 mark · Substitutes correct values for mass and volume in density equation
A1 (a) · 1 mark · Calculates correct density with correct unit
M2 (b) · 1 mark · Applies pressure = force / area and finds weight as force (F = mg)
A2 (b) · 1 mark · Uses correct area (0.2 × 0.10 m^2 = 0.02 m^2)
A3 (b) · 1 mark · Evaluates final pressure in pascals and gives correct answer to 2 sig fig
Worked solution
a) Volume = 0.2 × 0.10 × 0.05 = 0.001 m^3
Density = 2.5 kg / 0.001 m^3 = 2500 kg/m^3
b) Area in contact = 0.2 × 0.10 = 0.02 m^2