In a given system, there are both internal and external forces. Which of the following statements is true?

Question

a. The momentum of an object cant change unless an external force acts on the object

b) Internal forces like all forces always occur in action reaction pairs

c) Momentum conservation applies to all systems regardless of size

d) all of the above

Answer 1

a and c. Momentum of an object cannot change unless an external force acts on the object.

Internal forces all sum up to a zero resultant force. That is, no net external force results from the internal forces. So they are not action and reaction forces. The latter do not act on the same object but on two different objects.

Momentum conservation applies to all systems regardless of the size.