Question

An astronaut with a mass of `70 kg` is floating in space. If the astronaut throws an object with a mass of `8 kg` at a speed of `7/6 m/s`, how much will his speed change by?

Answer 1

I tried this:

Explanation:

We can use conservation of momentum before (throwing the object) and after (throwing the object) assuming that at the start the astronaut was at rest.
we get:

`0=m_("object")v_("object")+m_("astro")v_("astro")`

or:

`0=8*7/6+70*v_("astro")`

`v_("astro")=-(8*7/6)/70=-0.13m/s`

i.e. the speed of the astronaut will increase of `0.13m/s` in the opposite direction to the object.