# Conservation of Momentum and linear momentum

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## Homework Statement

In which one of the following situations is linear momentum not conserved?
A) A bomb suspended by a string explodes into one hundred fragments.
B) A bowling ball collides with ten pins.
C) A golf ball is struck by a club.
D) An astronaut floating in space throws a hammer away and subsequently moves in the opposite direction.
E) A tree limb is struck by lightning and falls to the ground.

## Homework Equations

Momentum=mass(velocity)

## The Attempt at a Solution

I have no idea... I thought momentum was always conserved? Can someone help explain this please? Thanks!

Homework Helper
do you know how to compute the momentum in the lightning bolt? (prolly not yet)
can you figure out a way to measure the Earth's speed moving up to meet the branch?
(Nobel prize if you do it)

Staff Emeritus
Homework Helper
Say you are standing on the the ground. You're at rest, so your momentum is zero. If you now jump, you rise through the air, and your momentum is no longer zero. Clearly, your momentum isn't conserved. However, look at the system consisting of you and the Earth. When you jump up, the Earth recoils, and the momentum of the system as a whole is conserved. Two cars colliding is another example. The momentum of an individual car is obviously not conserved, but the momentum of the two-car system is conserved. So the question of whether momentum is conserved or not depends on what you're talking about, on what is included in the system.