Question

When the rocket is on earth and lifting off and burning fuel, which of the following is or are conserved? Mark all that apply and provide a brief 1-2 sentence justification of your choices.  Momentum of the rocket  Mechanical energy of the rocket  Momentum of the rocket + exhaust + Earth system  Mechanical energy of the rocket + exhaust + Earth system When the rocket no longer burns fuel (but is still near Earth), which of the following is or are conserved? Mark all that apply and provide a brief 1-2 sentence justification of your choices.  Momentum of the rocket  Mechanical energy of the rocket  Momentum of the rocket + exhaust + Earth system  Mechanical energy of the rocket + exhaust + Earth system And I need a proper justification

Answer 1

First correct option is :

Momentum of the rocket + exhaust + Earth system

Reason : Only momentum or mechanical energy of rocket can not be conserved, since according to conservation principles, the momentum or energy lost or gained by the rocket, must be consumed or used by something else.

Also. since fuel is being burned, there is some lost in energy through heat. Thus, total mechanical energy, which is sum of kinetic and potential energy, is not conserved.So, only total momentum is being conserved.

Second correct options are :

Momentum of the rocket + exhaust + Earth system,

Mechanical energy of the rocket + exhaust + Earth system

Reason : Only momentum or mechanical energy of rocket can not be conserved, since according to conservation principles, the momentum or energy lost or gained by the rocket, must be consumed or used by something else.

Also, in this case, no fuel is being burned, so both momentum and total mechanical energy are being conserved.