# What are momentum and kinetic energy of m from the perspective of system 2?

Discussion in 'Physics' started by thexy, Feb 18, 2016.

1. ### thexy Thread Starter Member

Dec 13, 2015
126
0
From the perspective of system 1, the origin of system 2 moves with the velocity

, and a mass m with velocity

. What are momentum and kinetic energy of m from the perspective of system 2?

2. ### Kermit2 AAC Fanatic!

Feb 5, 2010
3,851
966
Your in a plane moving at velocity V. As you sit motionless in your chair on the plane, what do YOU perceive is your own velocity?

A moving system which uses itself as a reference frame cannot prove it is in motion. There needs to be a separate - second frame

3. ### BillO Distinguished Member

Nov 24, 2008
985
136
WRT to U2 v=(vx-ux, vy-uy, vz)

You should be able to figure the rest out from that.

4. ### WBahn Moderator

Mar 31, 2012
18,087
4,917
Reduce it to terms that you can imagine easily.

System one is a chair sitting next to the railroad track. The train is system 2. The train is moving to the left at 50 mph (relative to the chair) and a plane flies overhead left to right at 110 mph relative to the chair. What is the speed of the plane from the perspective of the train? Get that worked out using the mathematical notation above. Then got to a 2-D case where you are imagining a chair next to a lake and a boat moving out on the lake.