Question

An astronaut with a mass of `105` `kg` is floating in space. If the astronaut throws an object with a mass of `6` `kg` at a speed of `7/9` `ms^-1`, how much will his speed change by?

Answer 1

The initial momentum is `0` `kgms^-1`, and the final momentum will be the same because momentum is conserved.

The velocity of the astronaut will be `0.04` `ms^-1` in the opposite direction to the direction in which the object was thrown.

Explanation:

If we call the astronaut 'Object 1' and the object he throws 'Object 2', then momentum after the collision:

`p=m_1v_1+m_2v_2`

`0=105v_1+6xx7/9`

Rearranging:

`105v_1=-42/9`

`v_1=-0.04` `ms^-1`

The negative sign means the astronaut moves off in the opposite direction to the direction the object was thrown in, since we chose a positive sign for the velocity of the object.