Let us review about rocket move

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gema
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Hello Forum,

Let us review about rocket move.The Rocket moving with 2 mechanical principe;Newton's 3 and conservation of momentum.If rocket at t=0 is in rest condition (E=0),after the gas with dm mass go out to the back from rocket ,then rocket move to the front(E=Ek1+Ek2).
Nothing external force in this system,

Energy of system is conserve, if nothing external force in the system.
But why the energy of system isn't conserve?
 
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gema said:
Energy of system is conserve, if nothing external force in the system.
But why the energy of system isn't conserve?
What do you mean by 'energy is conserved'? Just because there are no external forces, doesn't mean mechanical energy (for example) is conserved. You are converting chemical energy into mechanical energy by burning the fuel. (Total energy is conserved of course.)