All objects experience a buoyancy when they are immersed in a fluid. Buoyancy is
- A.a downward force
- B.a downward pressure
- C.an upward force
- D.an upward pressure
Correct answer
Explanation
The correct answer is C, an upward force. Buoyancy, also called upthrust, is the upward force that a liquid or gas exerts on any object placed in it. It arises because pressure in a fluid increases with depth, so the fluid pushes harder on the bottom of an object than on its top, and the difference is a net force acting upwards. Archimedes' principle states that this buoyant force equals the weight of the fluid displaced by the object. If the buoyant force is greater than or equal to the object's weight, the object floats; if it is smaller, the object sinks. That is why an iron ship floats while an iron nail sinks. Option A is wrong because buoyancy opposes weight, which is the downward force. Option B is wrong because buoyancy is not downward and is a force, not a pressure. Option D is wrong because, although it comes from a pressure difference, buoyancy itself is measured as a force in newtons, not as a pressure in pascals. Exam tip: buoyant force = weight of fluid displaced (Archimedes); floats when upthrust ≥ weight.
Practice Questions
View allWhich one of the following is not used as fertilizer?
- A.Ammonium nitrate
- B.Ammonium sulphide
- C.Ammonium phosphate
- D.Ammonium sulphate
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Ammonium sulphide is an unstable, foul-smelling compound that breaks down to release ammonia and toxic hydrogen sulphide, so it is not used as a fertiliser.
Read the full explanation →The focal length of the objective lens of a telescope is 50 cm. If the magnification of the telescope is 25, then the focal length of the eye-piece is
- A.12.5 cm
- B.5 cm
- C.2 cm
- D.10 cm
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For an astronomical telescope in normal adjustment the magnifying power equals the focal length of the objective divided by that of the eyepiece, so the eyepiece focal length is 50 ÷ 25 = 2 cm.
Read the full explanation →The major source of vitamins and minerals for vegetarians is
- A.black gram and wheat.
- B.rice and mustard.
- C.vegetables and fruits.
- D.soya bean and milk.
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Vegetables and fruits supply most of the vitamins and minerals in a vegetarian diet, which is why they are called protective foods.
Read the full explanation →Which one of the following compounds is used in black and white photography?
- A.AgF
- B.AgBr
- C.AgCl
- D.Ag2SO4
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Silver bromide is the light-sensitive compound coated on black and white photographic film and paper, because light breaks it down into tiny grains of silver metal.
Read the full explanation →Which one of the following statements about speed and velocity is correct?
- A.Speed and velocity both are vector quantities.
- B.Speed and velocity both are scalar quantities.
- C.Speed is vector quantity and velocity is scalar quantity.
- D.Speed is scalar quantity and velocity is vector quantity.
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Speed tells only how fast a body moves, while velocity also tells the direction of motion, and a quantity with both magnitude and direction is a vector.
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