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This is a question from my homework.

Imagine an astronaut doing a repair in his ship, "parked" somewhere in space where gravity result is zero. As he can not do the repair, gets nervous and throws with all his might, the toolbox "down". What will happen to the astronaut? Why?

I wanna know what will happen to the astronaut? and why?

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No body knows the answer? Come on we're in a stack of physics. – Zignd May 7 '12 at 19:34
Is your astronaut playing music, or repairing his ship? xD – CHM May 7 '12 at 19:41
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@Igor: What is your question? What do you not understand? Please read the FAQ considering homework kind of questions physics.stackexchange.com/faq – Bernhard May 7 '12 at 19:45
ok, I guess now the question is understandable. – Zignd May 7 '12 at 19:52
Hi Igor - as Bernhard said, we don't allow questions that just ask for the answer to a homework problem. – David Zaslavsky♦ May 8 '12 at 4:56

closed as too localized by David Zaslavsky♦ May 8 '12 at 4:55

This question is unlikely to help any future visitors; it is only relevant to a small geographic area, a specific moment in time, or an extraordinarily narrow situation that is not generally applicable to the worldwide audience of the internet. For help making this question more broadly applicable, see the FAQ.

2 Answers

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Astronaut starts moving "up". Conservation of momentum.

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Thanks for the answer. I think it's because the astronaut will suffer the reaction exerted by the box. – Zignd May 7 '12 at 20:24
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These are two faces of the same coin. Conservation of momentum is direct consequence of III. Newton's law (with an assumption that no outer force acts on the system). – Pygmalion May 7 '12 at 20:26
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Two interacting bodies have the same forces in their equations, but of the opposite signs. So one body moves up and the other down:

$$m_1 \vec{a}_1=\vec{F}_{12}$$

$$m_2 \vec{a}_2=-\vec{F}_{12}$$

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