Question

A 70 kg astronaut floating in an orbiting space station throws a 1.0 kg water bottle across the room at a speed of 8 m/s. What is the magnitude of the astronaut's recoil velocity?

Answer 1

Use conservation of momentum. Initially momentum is zero, so after the throw

0 = m_astronaut v_astronaut + m_bottle v_bottle

=> v_astronaut = -(m_bottle / m_astronaut) v_bottle = -(1.0 kg / 70 kg)(8.0 m/s) = -0.114 m/s.

Magnitude = 0.11 m/s (opposite the bottle's direction).