physics-mechanics

你可以參考我昨天答的回答：

http://hk.knowledge.yahoo.com/question/question?qid=7009032900791


The answer is C.

There is no external force acting on the system. Therefore the total momentum of the system must conserve. And hence the total momentum remains unchanged.

Initially the object is at rest, in which the total kinetic energy is zero. But after the explosion, the two fragments move with a certain speed in opposite directions.

But kinetic energy is a scalar, so as long as the parts have non-zero speed, the K.E. is larger than zero. Hence the total kinetic energy increases.