Engineering Physics Multiple Choice Questions on “Coefficient of Restitution”.
1. A body can have momentum without energy.
a) True
b) False
Answer: b
Clarification: If a body has momentum, it must be in motion and consequently possess kinetic energy. Therefore a body cannot have momentum without energy.
2. Comets mover around the sun in highly elliptical orbits. The gravitational force on the comet due to the sun is not normal to the comet’s velocity in general. Yet the work done by the gravitational force over every orbit of the comet is zero. Why?
a) The gravitational force is conservative, hence work done is zero
b) The gravitational force is non-conservative, hence work done is zero
c) Energy is absent, hence work done is zero
d) Force is in negative direction
Answer: a
Clarification: The gravitational force acting on the comet is a conservative force. The work done by a conservative force is equal to the negative of the change in potential energy. Over a complete orbit of any shape, there is no change in potential energy of the comet. Hence no work is done by the gravitational force on the comet.
3. An artificial satellite orbiting the earth in very thin atmosphere loses its energy gradually due to dissipation against atmospheric resistance, however small. As it comes closer and closer to earth, its speed ___________
a) Decreases progressively
b) Remains constant
c) Becomes non-uniform
d) Increases progressively
Answer: d
Clarification: As the satellite comes closer to the earth, its potential energy decreases. As the sum of kinetic energy and potential energy remains constant, the kinetic energy and the velocity of the satellite increase. But the total energy of the satellite goes on decreasing due to the loss of energy against friction.
4. In an inelastic collision, the final kinetic energy is always less than the initial kinetic energy of the system.
a) True
b) False
Answer: a
Clarification: In an inelastic collision, a part of the initial kinetic energy of the system always changes into some other form of energy.
5. In which of the following the momentum and energy of each body not conserved?
a) Inelastic collision
b) Oblique collision
c) Elastic collision
d) Head on collision
Answer: c
Clarification: Inelastic collision, total momentum and total energy of the entire system are conserved and not individual bodies.
6. In an elastic collision of two billiard balls, the total kinetic energy is conserved ___________
a) Completely
b) For a short duration
c) For a long duration but not completely
d) Never
Answer: b
Clarification: During the short time of collision when the balls are in contact, the kinetic energy of the balls gets converted into the potential energy. In an elastic collision, though the kinetic energy before the collision is equal to the kinetic energy after the collision but kinetic energy is not conserved during the short time of collision.
7. Which of the following is an example for a force which does work on a body but fails to change its kinetic energy?
a) A body pulled through a plain surface
b) A body pulled through a vertical surface
c) A body pulled through a horizontal surface
d) A body at rest
Answer: c
Clarification: When a body is pulled through a rough horizontal surface with constant velocity, work is done by the applied force on the body but the kinetic energy of the body remains unchanged.
8. The mechanical energy of a system is always conserved.
a) True
b) False
Answer: b
Clarification: The mechanical energy is conserved only when conservative forces are involved and the system should be isolated. Thus the mechanical energy is not always conserved.
9. Two masses of 1g and 4g are moving with equal kinetic energy. The ratio of the magnitudes of their momenta is ___________
a) 4:1
b) √2:1
c) 1:2
d) 1:16
Answer: c
Clarification: p = √2mK
For same K, (frac{P_1}{P_2} = sqrt{frac{m_1}{m_2}} = frac{1}{2}) = 1:2.
10. If a machine is lubricated with oil ___________
a) The mechanical advantage of the machine increases
b) The mechanical efficiency of the machine increases
c) Both its mechanical advantage and efficiency increases
d) Its efficiency increases, but its mechanical advantage decreases
Answer: b
Clarification: When a machine is lubricated with oil, energy wastage against friction decreases. This increases the mechanical efficiency of the machine.