SAT Subject Physics Practice Question 319: Answer and Explanation
15. A rocket is launched into the air during a fireworks show. Which of the following statements about the parts of the rocket is appropriate immediately after the explosion?
A. They have less mass than they had before the explosion.
B. They have more momentum than they had before the explosion.
C. They have less momentum than they had before the explosion.
D. They have the same momentum as they had before the explosion.
E. They have less kinetic energy than they had before the explosion.
Correct Answer: D
The correct answer is (D). The momentum before the explosion must equal the momentum after the explosion. Initially, the momentum of the parts was zero; therefore, all the parts moving in all directions could be added together, and they would equal the momentum before the explosion: zero!