Which of the following statements about a fluid at rest in a cup is/are correct? 1. Pressure is same at all the points in the fluid 2. Pressure is exerted on the walls. 3. Pressure exists everywhere in the fluid. Select the correct answer using the code given below :
- A.1 and 2 only
- B.2 and 3 only
- C.1 only
- D.1, 2 and 3
Correct answer
Explanation
The correct answer is B, 2 and 3 only. A fluid at rest presses on the walls and has pressure at every point, but that pressure is not the same at all depths.
The pressure at a depth h in a liquid at rest is P = P₀ + hρg, where P₀ is the air pressure on the surface and ρ the density of the liquid. So pressure rises steadily with depth and is greatest at the bottom of the cup. It is the same only at points on one horizontal level. A fluid at rest also pushes at right angles on every surface it touches, including the walls of its container, which is why water spurts out further from a hole lower down a bottle.
A is wrong because statement 1 is false: pressure increases with depth.
C is wrong because statement 1 alone is the one false statement.
D is wrong because it includes the false statement 1.
Exam tip: P = hρg, so pressure grows with depth and is equal only at the same level; it acts on the walls and in all directions.
Practice Questions
View allThe absolute zero temperature is 0 Kelvin. In °C unit, which one of the following is the absolute zero temperature?
- A.0 °C
- B.-100 °C
- C.-273.15 °C
- D.-173.15 °C
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Zero on the Kelvin scale lies 273.15 degrees below the freezing point of water. The Kelvin and Celsius scales have degrees of the same size, so T(K) = t(°C) + 273.15.
Read the full explanation →Dinitrogen (N₂) and dioxygen (O₂) are the main constituents of air but they do not react with each other to form oxides of nitrogen because
- A.the reaction requires initiation by a catalyst
- B.oxides of nitrogen are unstable
- C.the reaction is endothermic and requires very high temperature
- D.the stoichiometry of N₂ and O₂ in air is not ideal for the reaction to take place
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Nitrogen and oxygen combine only when a lot of energy is supplied. The nitrogen molecule is held by a very strong triple bond, so breaking it takes much energy, and the reaction N₂ + O₂ → 2NO absorbs heat.
Read the full explanation →Hydrogenation of vegetable oils using nickel catalyst is an example of
- A.Substitution reaction.
- B.Elimination reaction.
- C.Addition reaction.
- D.Free-radical polymerization.
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Hydrogen adds across the carbon–carbon double bonds of the oil. Vegetable oils are unsaturated: their fatty acid chains contain C=C double bonds, which keep them liquid.
Read the full explanation →A positive charge is moving towards south in a space where magnetic field is pointing in the north direction. The moving charge will experience :
- A.a deflecting force towards north direction.
- B.a deflecting force towards east direction.
- C.a deflecting force towards west direction.
- D.no deflecting force.
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The charge moves exactly opposite to the field, and a magnetic field exerts no force on a charge moving along its line.
Read the full explanation →Which one of the following about different frictional forces is correct?
- A.Kinetic friction > Static friction > Rolling friction
- B.Static friction > Rolling friction > Kinetic friction
- C.Static friction > Kinetic friction > Rolling friction
- D.Static friction > Kinetic friction = Rolling friction
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It takes most force to start an object moving, less to keep it sliding and least to keep it rolling.
Read the full explanation →