A ball balanced on a vertical rod is an example of
- A.stable equilibrium
- B.unstable equilibrium
- C.neutral equilibrium
- D.perfect equilibrium
Correct answer
Explanation
The correct answer is B, unstable equilibrium. The slightest push makes the ball fall off and it does not come back.
A body is in unstable equilibrium when a small displacement lowers its centre of gravity, so the forces acting on it move it further away instead of back. A ball on the tip of a rod sits at its highest possible point; once it is tipped, its weight acts outside the small base and it rolls off. A pencil standing on its point and a cone on its tip are other examples.
A is wrong because in stable equilibrium the body returns to its position when disturbed, like a ball at the bottom of a bowl.
C is wrong because in neutral equilibrium the body stays in its new position, like a ball on a flat floor.
D is wrong because perfect equilibrium is not one of the three standard types.
Exam tip: disturbed body returns = stable; moves further away = unstable; stays where placed = neutral. Low centre of gravity and wide base mean more stability.
Practice Questions
View allThe pressure exerted by a 760 mm column of mercury at 0 °C is known as
- A.1 pascal
- B.1 atmosphere
- C.1 bar
- D.1 poise
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Standard atmospheric pressure at sea level is defined as the pressure of a 760 mm column of mercury at 0 °C. In 1643 Evangelista Torricelli showed that air pressure holds up a column of mercury about 760 mm (76 cm) tall in a glass tube, inventing the mercury barometer.
Read the full explanation →Sound and light waves are
- A.respectively longitudinal and transverse in air
- B.respectively transverse and longitudinal in air
- C.both longitudinal in air
- D.both transverse in air
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Sound travels as compressions and rarefactions, while light is a transverse electromagnetic wave. In a longitudinal wave the particles of the medium vibrate back and forth along the direction in which the wave moves.
Read the full explanation →Which one of the following is the purest form of Carbon ?
- A.Charcoal
- B.Coke
- C.Fullerene
- D.Carbon black
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Fullerenes are made of carbon atoms alone, with no surface to trap other substances, so they are counted as the purest form of carbon.
Read the full explanation →A planet has a mass M₁ and radius R₁. The value of acceleration due to gravity on its surface is g₁. There is another planet 2, whose mass and radius both are two times that of the first planet. Which one of the following is the acceleration due to gravity on the surface of planet 2?
- A.g₁
- B.2g₁
- C.g₁/2
- D.g₁/4
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Surface gravity is g = GM/R², so doubling the mass doubles g while doubling the radius divides it by four, leaving g₁ × 2/4 = g₁/2.
Read the full explanation →Which one of the following is the major constituent of biogas ?
- A.Carbon dioxide
- B.Nitrous oxide
- C.Methane
- D.Oxygen
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Methane makes up the largest share of biogas, usually about 55 to 75 per cent, and it is the gas that burns.
Read the full explanation →