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CAIE A-Level Physics 4.3.5 How Fluid Pressure Produces Upthrust

Practise explaining upthrust from greater pressure below an immersed object, relating pressure difference to upward force and applying force balance.

Syllabus
2028–2030
Course
Physics 9702
Level
AS

Exam points

  • explain that upthrust is caused by the greater hydrostatic pressure on the lower surface than on the upper surface
  • relate the pressure difference across an immersed object to the magnitude and upward direction of the resultant force
  • use force diagrams or equilibrium conditions to determine whether upthrust supports, accelerates or balances an object in a fluid

4.3.5—The upthrust acting on an object in a fluid is due to a difference in question 1

[Maximum number: 2]

The cylinder is now immersed in water, as illustrated in Fig. 3.2.

Fig. 3.2

Fig. 3.2

An upthrust acts on the cylinder and the bar is not in equilibrium.

Explain the origin of the upthrust.

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