Question

An astronaut with a mass of `85 kg` is floating in space. If the astronaut throws a `17 kg` object at a speed of `15 m/s`, how much will his speed change by?

Answer 1

Net momentum must remain the same. Momentum is given by the equation `p=mv`, at the beginning the astronaut is at rest so his velocity and therefore his momentum are `0`. The final momentum of the system must then also be `0`. Throwing an object with a mass of `"17 kg"` and a velocity of `15"m"/"s"` gives that object a momentum of `"17 kg"xx15"m"/"s"=255 ("kg"*"m")/("s")`.

So the astronaut has to move in the opposite direction with the same momentum for the net momentum to be `0`, they have to cancel out. Solve the equation `255 ("kg"*"m")/("s")="85 kg"xxv`.

`v=(255 ("kg"*"m")/("s"))/"85 kg"=3"m"/"s"`.

Therefore his change in speed is `3"m"/"s"`.