The acceleration due to gravity at the Earth's surface depends on
- A.its mass only.
- B.its radius only.
- C.both its mass and radius.
- D.either its mass or its radius.
Correct answer
Explanation
The correct answer is C, both its mass and radius. By Newton's law of gravitation, the acceleration due to gravity at the surface is g = GM/R², where G is the universal gravitational constant, M is the mass of the Earth and R is its radius. So g rises with the planet's mass and falls with the square of its radius. For the Earth this gives about 9.8 m/s². The same formula explains everyday facts: g is slightly larger at the poles than at the equator because the polar radius is smaller, and g decreases as we go up a mountain or deep into a mine. It also explains why g on the Moon is only about one-sixth of the Earth's value. Importantly, g does not depend on the mass of the falling body. Option A is wrong because the radius also appears in the formula. Option B is wrong because the mass is equally necessary. Option D is wrong because g needs both quantities together, not either one. Exam tip: g = GM/R², about 9.8 m/s², highest at the poles.
Practice Questions
View allWhich one of the following plant tissues has dead cells ?
- A.Epidermis
- B.Parenchyma
- C.Collenchyma
- D.Sclerenchyma
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Sclerenchyma cells are dead at maturity, with thick walls hardened by lignin. Sclerenchyma is the tissue that makes plants hard and stiff.
Read the full explanation →Imagine a current-carrying straight conductor with magnetic field of lines in anti-clockwise direction. Then the direction of current is determined by
- A.the Right-Hand Thumb rule and it would be in the downward direction.
- B.the Left-Hand Thumb rule and it would be in the downward direction.
- C.the Right-Hand Thumb rule and it would be in the upward direction.
- D.the Left-Hand Thumb rule and it would be in the upward direction.
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For a straight wire, the right-hand thumb rule links the current to the circular field lines around it. Hold the wire in the right hand with the thumb along the current; the curled fingers then show the direction of the magnetic field lines, which form concentric circles around the wire.
Read the full explanation →Which one of the following statements is true for sound waves propagating in air?
- A.Sound is an electromagnetic wave and transverse in nature
- B.Sound is a mechanical wave and longitudinal in nature
- C.Sound is a mechanical wave and transverse in nature
- D.Sound is an electromagnetic wave and longitudinal in nature
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Sound needs a material medium to travel, and in air its particles vibrate back and forth along the direction the wave moves.
Read the full explanation →Which one of the following is primarily responsible for conduction of current in a metal?
- A.Bound electrons
- B.Free electrons
- C.Both bound and free electrons
- D.Ions
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In a metal, the outer electrons of the atoms are not tied to any one atom and drift through the lattice when a voltage is applied, carrying the current.
Read the full explanation →Which one of the following statements is correct about the magnification of an optical microscope?
- A.Magnification increases with the increase in focal length of eyepiece
- B.Magnification increases with the increase in focal length of objective
- C.Magnification does not depend upon the focal length of eyepiece
- D.Magnification decreases with the increase in focal length of eyepiece
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A compound microscope magnifies more when both its lenses have short focal lengths. In a compound microscope the objective forms a real, enlarged image, and the eyepiece magnifies it further like a simple magnifier.
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