Complete the following statement: Momentum will be conserved in a two-body collision only if a both bodies come to rest. b the internal forces of the two body system cancel in action-reaction pairs. c the kinetic energy of the system is conserved. d the net external force acting on the two-body system is zero. e the collision is perfectly elastic.

d the net external force acting on the two-body system is zero

Explanation:

The net external force acting on the two-body system is zero .

During a collision , two internal forces appear on two bodies in opposite directions separately . As they act on each object separately , they do not cancel each other . But the net force on two body system is zero . Total momentum is always conserved during collision because no external force is involved . Collision is not always elastic .

reserve is the answer

conservation of mass

mass before something happens = mass afterwards