- #1
Hunter235711
- 14
- 1
This is a problem I have never really understood. If a rocket engine is fired in a vacuum, does it exert the same force regardless of its velocity? If so, I don't know how to get around the following issue.
Say that the chemical energy stored in a particular rocket engine is 100 Joules (I am just making these numbers up). Also, assume the rocket exerts a 10 Newton force for 3 seconds when fired. Now, if this rocket engine were mounted on a spaceship traveling at 1 meter per second it would release 3seconds*1meter/second*10Newtons = 30 Joules of energy when fired. No problem here, engine is about 30% efficient. However, now assume the spaceship is traveling at 100 meters per second. Now the same engine is fired and releases 3seconds*100meters/second*10Newtons = 3000 Joules! But this is impossible because the total chemical energy liberated by the rocket engine was only 100 Joules.
What is wrong with my logic? Thanks for your help!
Hunter
Say that the chemical energy stored in a particular rocket engine is 100 Joules (I am just making these numbers up). Also, assume the rocket exerts a 10 Newton force for 3 seconds when fired. Now, if this rocket engine were mounted on a spaceship traveling at 1 meter per second it would release 3seconds*1meter/second*10Newtons = 30 Joules of energy when fired. No problem here, engine is about 30% efficient. However, now assume the spaceship is traveling at 100 meters per second. Now the same engine is fired and releases 3seconds*100meters/second*10Newtons = 3000 Joules! But this is impossible because the total chemical energy liberated by the rocket engine was only 100 Joules.
What is wrong with my logic? Thanks for your help!
Hunter