A little physics riddle - Lemmy.ca

cross-posted from: https://lemmy.ca/post/33867210 [https://lemmy.ca/post/33867210] > Here’s a little physics riddle. It’s really meant as a moment of self-reflection for physics teachers (I invite you to compare what answers you’d give within Relativity Theory). > > We’re in the context of Newtonian mechanics. > > There are three small bodies. In the inertial coordinate system (t, x, y, z), we know the following about the three bodies (at a given instant of time): > > - The first has mass 3 kg > - The second has velocity (1, 0, 0) m/s > - The third has momentum (2, 0, 0) kg⋅m/s > > Now consider a new coordinate system (t’, x’, y’, z’) related to the first by the following transformation (a Galileian boost): > > t’ = t, x’ = x - u⋅t, y’ = y, z’ = z > with u = 1 m/s > > Questions: > > - What is the mass of the first body in the new coordinate system? > - What is the velocity of the second body in the new coordinate system? > - What is the momentum of the third body in the new coordinate system? > > Can you give definite answers to these three questions, and motivate your answers with simple physical principles? Note that by “definite answer” I don’t necessarily mean an answer with a definite numerical value.