The laws of thermodynamics state that, in a heat engine, energy flows from a cold source to a warm target all the heat energy from a source cannot be converted to mechanical energy all the heat energy from a source must be converted to mechanical energy entropy cannot change during heat flow

The correct option is "all the heat energy from a source cannot be converted to mechanical energy"

Explanation:

Heat engine is a system which converts heat energy to the mechanical energy. During this process, a lot of heat energy is lost to surrounding.

Heat engine is a device that uses heat to do work. It is impossible to extract an amount of heat from the reservoir at high temperature and use this heat to do some work.

Some heat is rejected to the reservoir at low temperature.

Therefore, the laws of thermodynamics state that, in a heat engine, all the heat energy from a source cannot be converted to mechanical energy.

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