Which one of the following is not a conservative force ?
- A.Frictional force
- B.Electric force
- C.Gravitational force
- D.Spring force
Correct answer
Explanation
The correct answer is A, Frictional force. Friction is a non-conservative force because the work it does depends on the path taken and the energy it removes is lost as heat.
A force is conservative when the work it does in moving a body between two points does not depend on the path, and the work over any closed path is zero. Such a force has a potential energy linked to it, so mechanical energy is conserved. Friction always acts against the motion: drag a box around a room and back to the start and friction has done negative work all the way, turning kinetic energy into heat. Air resistance and viscous drag are also non-conservative.
B is wrong: the electrostatic force between charges is conservative and has electric potential energy. C is wrong: gravity is the standard example of a conservative force; work done against it is stored as gravitational potential energy. D is wrong: the spring force obeys Hooke's law and stores elastic potential energy of ½kx².
Exam tip: Conservative: gravitational, electrostatic, spring force; non-conservative: friction, air resistance, viscous force.
Practice Questions
View allA negative work is done when an applied force F and the corresponding displacement S are
- A.perpendicular to each other.
- B.parallel to each other.
- C.anti-parallel to each other.
- D.equal in magnitude.
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Work is negative when the force acts opposite to the displacement, because the angle between them is then 180°. Work done is W = F S cos θ, where θ is the angle between the force and the displacement.
Read the full explanation →Which one of the following statements about a satellite orbiting around the Earth is correct ?
- A.Satellite is kept in orbit by remote control from ground station.
- B.Satellite is kept in orbit by retro-rocket and solar energy keeps it moving around the Earth.
- C.Satellite requires energy from solar panels and solid fuels for orbiting.
- D.Satellite does not require any energy for orbiting.
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Once a satellite is placed in orbit with the right speed, the Earth's gravity keeps it going round without any engine.
Read the full explanation →A microphone converts
- A.electrical signals to sound waves
- B.sound waves to electrical signals
- C.microwaves to sound waves
- D.sound waves to microwaves
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A microphone is a transducer that changes the pressure variations of sound into a matching electrical signal. In a common dynamic microphone, sound waves make a thin diaphragm vibrate.
Read the full explanation →When a light ray passes through from air to water with a non-zero angle the ray will be
- A.bending towards the normal
- B.bending away from the normal
- C.propagating in straight line
- D.reflected towards the opposite direction
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Light slows down when it enters water from air, so a ray that strikes the surface at an angle bends towards the normal.
Read the full explanation →Light year is a measure of
- A.time
- B.distance
- C.total amount of light falling on the Earth in a year
- D.average intensity of light falling on the Earth in a year
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A light year is the distance that light travels in empty space in one year, so despite the word "year" it measures length, not time.
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