# Object in a vacuum

1. Feb 23, 2010

### Daagon

Hey guys,

I have a question; I was in a Physics lesson at school today, me and my teacher got into a discussion about space and vacuums. Somehow we managed to get marsh mellows into te convosation, and my mind wondered until I came up with this question -

If a Marshe Mellow is traveling in a Vacuum (space), nothing can stop it, (an object in motion would stay in motion in a vacuum, as there is nothing to interfere). So if it them hit a larger object, like a Human, they would both have the same mass in space, so would the marshe mellow hit the human and take him/her along with it, or would the human act as an interference and slow the marshe mellow down?

Thanks guys!

-Samuel

2. Feb 23, 2010

### Mapes

Hi Daagon, welcome to PF. There's a physical law (called the conservation of linear momentum) that says that the total momentum (mass times velocity, mv) is constant in any isolated system. It's perfect for analyzing this question.

Say a human with mass $m_H$ is initially motionless, with zero velocity, and the marshmellow comes along with mass $m_M$ and velocity $v_M$ and sticks to the human. We can write

[tex]m_M v_M=(m_{M+H})(v_{M+H})[/itex]

because the total momentum is the same before and after the collision. Can you answer your question now?