Question

Which of the following statement is/are true?

• A. In a elastic collision of two bodies, the momentum and energy of each body is conserved.
• B. The total energy of a system is always conserved irrespective of whether external forces act on the system.
• C. The work done by a force in nature on a body, over a closed loop, is not always zero.
• D. In an inelastic collision of two bodies, the final kinetic energy is less than the initial kinetic energy of the system.

Answer 1

Answer: (C), (D)

In an inelastic collision of two bodies, the final kinetic energy is less than the initial kinetic energy of the system.

Choice (a) is false. In an elastic collision of two bodies, the speeds of the bodies change due to collision.
Therefore, the momentum and energy of each body will change but the total momentum and total energy of the system of two bodies are conserved.
Choice (b) is also false. The total energy of an isolated system is conserved. If external forces act on the system, the total momentum and energy will change.
Choice (C) is true. For a non-conservative force such as friction, the work done over a closed loop is not zero, where as for conservative forces it is always zero
Choice (d) is also true. In an inelastic collision, part of initial kintic energy will be lost in the form heat, sound energy . Hence choices (c) and (d) are correct.