Weight and mass of an object are defined with Newton's laws of motion. Which among the following is true ?
- A.Weight is a constant of proportionality.
- B.Mass is a constant of proportionality.
- C.Mass is not a constant of proportionality.
- D.Weight is a universal constant.
Correct answer
Explanation
The correct answer is B, Mass is a constant of proportionality. In Newton's second law, F = ma, the force on a body is proportional to its acceleration, and the constant linking the two is the body's mass.
By Newton's second law, F = ma: double the force and the acceleration doubles, while the mass stays the same and measures the body's inertia, its resistance to a change in motion. Mass is a scalar, measured in kilograms, and does not change from place to place. Weight is the force of gravity on the body, W = mg, measured in newtons. It changes with g, so an astronaut weighs about one-sixth as much on the Moon though the mass is unchanged.
A is wrong because weight is itself a force, W = mg, not the constant that links force and acceleration. C is wrong because it denies the role mass plays in F = ma. D is wrong because weight varies with gravity and is not a universal constant like G.
Exam tip: mass – kilogram, constant, measure of inertia; weight – newton, W = mg, changes with g.
Practice Questions
View allWhich one of the following is monatomic?
- A.Hydrogen
- B.Sulphur
- C.Phosphorus
- D.Helium
Show answer
A monatomic element exists as single, separate atoms. Helium is a noble gas of group 18: its only shell, the first, is full with two electrons, so a helium atom has no tendency to share or transfer electrons and does not bond even with another helium atom.
Read the full explanation →The normal systolic pressure in human beings is :
- A.80 mm of Hg
- B.100 mm of Hg
- C.120 mm of Hg
- D.140 mm of Hg
Show answer
Blood pressure is written as two numbers, and normal adult blood pressure is about 120/80 mm of mercury.
Read the full explanation →'Study of human societies and cultures from the oldest times to the present' is the work of
- A.Archaeologists
- B.Anthropologists
- C.Palaeontologists
- D.Geologists
Show answer
Anthropology, from the Greek 'anthropos' (human) and 'logos' (study), is the science of human beings: how societies and cultures began, how they changed and how people live today.
Read the full explanation →Which of the following catalytic systems is used for the reduction of unsaturated hydrocarbon to saturated hydrocarbon?
- A.Copper and H2
- B.Iron and H2
- C.Zinc and H2
- D.Nickel and H2
Show answer
Adding hydrogen across the double or triple bond of an alkene or alkyne turns it into a saturated alkane; this reaction is called hydrogenation and it needs a catalyst.
Read the full explanation →Which one among the following is not a plant hormone ?
- A.Gibberellins
- B.Abscisic acid
- C.Auxins
- D.Thyroxine
Show answer
Thyroxine is an animal hormone, made by the thyroid gland in the neck, and it controls the rate of metabolism in the human body.
Read the full explanation →