When a body does some work its energy decreases.
(b) Work done by a body against friction always results in a loss of its kinetic / potential energy.
(c) The rate of change of total momentum of a many-particle system is proportional to the external force / sum of the internal forces on the system.
A heat engine undergoes a process in which its internal energy decreases by 400 J and it gives out 150 J of heat. During the process: