We're almost positive that Newton's laws of motion are true near Alpha Centauri, just as much as they're true here in OUR neighborhood. So we can use Newton's 2nd law, and assume that
Force = (mass) x (acceleration).
(15 N) = (mass) x (7 m/s²)
We're also confident that elementary algebra works out there too, so we can divide each side of this equation by (7 m/s²). Then it says ...
Mass = (15 N) / (7 m/s²)
Mass = (15/7) (N-s²/m)
Mass = 2.143 kg
