A sealed monitoring instrument is calibrated in two stationary liquids. The instrument has horizontal upper and lower plates, each with an area of 0.010 m2. The vertical distance between the plates is 0.30 m.
During each test, the liquid completely surrounds the instrument. The instrument is symmetrical, so the forces on its side surfaces cancel.
The table gives the density of each liquid and the pressure due to the liquid at the upper plate.
| Liquid | Density in kg m−3\mathrm{kg\,m^{-3}}kgm−3 | Pressure at upper plate in kPa\mathrm{kPa}kPa |
|---|---|---|
| X | 900 | 13.5 |
| Y | 1200 | 18.0 |
The weight of the instrument is 31 N.
Take g=10 N kg−1g=10\ \mathrm{N\,kg^{-1}}g=10 Nkg−1.
Calculate the pressure due to the liquid at the lower plate in each liquid.
Calculate the upthrust on the instrument in each liquid.
The instrument is released from rest in each liquid. Explain how it starts to move in liquid X and in liquid Y.
132 exam-style questions on Edexcel GCSE Physics 15.2 Pressure in fluids, covering 15.2.1 Atmospheric pressure and height, 15.2.2 Pressure in fluids, 15.2.3 Pressure, force and area, 15.2.4 Pressure and depth, 15.2.5 Pressure in liquids: depth and density, 15.2.6 Upthrust, and 15.2.7 Floating and sinking. Each one has a worked solution and a mark scheme showing where the marks go.