4. Joule's insight was to say simply that the only factors affecting the amount of work done are the size of the force, and how far the object is moved in the direction of the force .
42. In all collisions and explosions momentum is conserved if no external force acts.
43. In elastic collisions the total kinetic energy of the system is also conserved.
44. In inelastic collisions the total kinetic energy is not conserved; some energy will be transferred to sound, internal energy or stored as elastic energy.
45. In an explosion , the total momentum is always zero.