How many stars in the star rating label of an electrical appliance should be used? Explain your answer.
1 answer:
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Answer:
Approximately .
Explanation:
Let the increase in the rocket's velocity be . Let
represent the initial velocity of the rocket. Note that for this question, the exact value of
doesn't really matter.
The momentum of an object is equal to its mass times its velocity.
- Mass of the rocket with the 5 kg of fuel:
.
- Initial velocity of the rocket and the fuel:
.
- Hence the initial momentum of the rocket:
.
- Mass of the rocket without that 5 kg of fuel:
.
- Final velocity of the rocket:
.
- Hence the final momentum of the rocket:
.
- Mass of the 5 kg of fuel:
.
- Final velocity of the fuel:
(assuming that the the 500 m/s in the question takes the rocket as its reference.)
- Hence the final momentum of the fuel:
.
Momentum is conserved in an isolated system like the rocket and its fuel. That is:
Sum of initial momentum = Sum of final momentum.
.
Note that appears on both sides of the equation. These two terms could hence be eliminated.
.
.
Hence, the velocity of the rocket increased by around 2.5 m/s.