Pressure under a Solid
4 marks · NormalA rectangular block of wood has a mass of 4.5 kg. It is placed flat on the ground so that it touches the floor with its largest face. The area of this face is 0.3 m².
Calculate the weight of the block. (Take g = 10 N/kg.)
Calculate the pressure the block exerts on the ground. Give the unit.
If the block is stood on its smallest face of area 0.05 m², calculate the new pressure exerted on the ground.
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.
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(a) 45 N
(b) 150 Pa
(c) 900 Pa
Common mistakes: confusing area values; not converting mass to weight
Show mark scheme and worked solution
Marking points
M1 (a) · 1 mark · Calculate weight as mass × g.
M2 (b) · 1 mark · Use p = F/A with correct values. (follow-through)
A1 (b) · 1 mark · Obtain correct pressure for first area (150 Pa) with unit. (follow-through)
A2 (c) · 1 mark · Obtain correct pressure for second area (900 Pa) with unit. (follow-through)
Worked solution
a) Weight = mass × g = 4.5 kg × 10 N/kg = 45 N
b) Pressure = force / area = 45 N / 0.3 m² = 150 Pa
c) New pressure = 45 N / 0.05 m² = 900 Pa