Question

A firecracker at rest explodes, sending fragments off in all directions. Initially the
firecracker has zero momentum, but after the explosion the fragments flying off each other have quite a lot
of momentum. Hasn't momentum been created? If not, explain why not?
[2]
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Answer 1

Answer:

You have to understand that momentum is a vector quantity. So you need to account for direction and speed.

If you consider both the product of mass and speed in a particular direction, then you are calculating momentum

Momentum = mass x speed in a given direction.

Now imagine that you limit an explosion to only two dimensions by supplying a top and bottom surface. Then you could represent the speed of each particle using x and y components.

If you calculate all the x components you will find that the total x components of momentum do cancel out so that total x components add to zero.

Simarly for y components.

So, since momentum is a vector quantity, the total momentum before equal s zero and that is the vector sum of the momenta after explosion too.