Density and Pressure
4 marks · EasyA student wants to find the density of a small stone. She measures the mass of the stone as 45 g, and the volume of water displaced by the stone is 16 cm³.
State the equation used to calculate density.
Calculate the density of the stone in g/cm³.
Explain why the student used water displacement to measure the volume.
If the stone is placed at the bottom of a container and rests on an area of 3.0 cm², calculate the pressure it exerts on the bottom (in Pa). (Take g = 10 N/kg.)
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) density = mass / volume
(b) 2.81 g/cm³
(c) Because the stone has an irregular shape, so its volume cannot be measured directly.
(d) 1500 Pa
Common mistakes: Forgetting unit conversions; Using g instead of mass in pressure
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · States correct equation for density (words or symbols).
A1 (b) · 1 mark · Accurate calculation of density in g/cm³.
B2 (c) · 1 mark · States a correct reason for using water displacement for irregular objects.
A2 (d) · 1 mark · Correct calculation of pressure in pascals.
Worked solution
a) The equation is: density = mass / volume
b) mass = 45 g, volume = 16 cm³
c) Water displacement is used because the stone is irregular and its volume can't be measured using a ruler.
d) Convert mass to kg: 45 g = 0.045 kg. Weight = 0.045 × 10 = 0.45 N. Area = 3.0 cm² = 3.0 × 10⁻⁴ m². Pressure = 0.45 / 3.0×10⁻⁴ = 1500 Pa.