1. 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
Explanation: 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.
2. In an inelastic collision, the final kinetic energy is always less than the initial kinetic energy of the system.
a) True
b) False
Explanation: In an inelastic collision, a part of the initial kinetic energy of the system always changes into some other form of energy.
3. 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
Explanation: Inelastic collision, total momentum and total energy of the entire system are conserved and not individual bodies.
4. 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
Explanation: 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.
5. 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
Explanation: 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.
6. The mechanical energy of a system is always conserved.
a) True
b) False
Explanation: 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.
7. 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
Explanation: p = √2mK
For same K, \(\frac{P_1}{P_2} = \sqrt{\frac{m_1}{m_2}} = \frac{1}{2}\) = 1:2.
8. 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
Explanation: When a machine is lubricated with oil, energy wastage against friction decreases. This increases the mechanical efficiency of the machine.
9. Internal force is responsible for the change in velocity of an object.
a) True
b) False
Explanation: The outside force exerted on an object by an external agency is called an external force. Such a force changes the velocity of an object.
10. Internal force holds together the particles as a single object.
a) True
b) False
Explanation: The mutual forces exerted by the particles of a system on one another are called internal forces. These forces are responsible for holding together the particles as a single object.