Which one among the following statements is correct?
The total mechanical energy of a system is conserved if the forces, doing work on it, are conservative.
The law of conservation of mechanical energy applies only when the net work done on a system is by conservative forces (such as gravity or an ideal spring force), for which a well-defined potential energy can be assigned; under this condition the sum of kinetic and potential energy stays constant.
If non-conservative forces (like friction or air resistance) do work, mechanical energy is not conserved — some of it is dissipated as heat, so the second option is false, and the third option (that mechanical energy always remains constant, unconditionally) is also false.
Not every force has an associated potential energy — non-conservative forces such as friction do not, since the work they do depends on the path taken, so the fourth option is false.
Hence, the correct statement is that total mechanical energy is conserved when the forces doing work are conservative.
Important Questions from Work Power Energy
Which of the following is NOT correct regarding friction?
If a pump can raise 200 liters of water through a height of 300 meters in one minute, how much work can it do in one hour?
Which of the following is an example of kinetic energy?
How much kinetic energy does a 160 g cricket ball have when it is thrown at a speed of 22 m/s?
The movement of birds is an example of _______.
