Which is always true in a closed system? Acceleration is not constant.
Mass is not conserved.
Momentum is conserved.
Velocity is constant.

The correct option is momentum is conserved

Explanation:

A closed system is a system that is independent/free of external factors/force and does not exchange matter with its surrounding. Since a close system is free of external factors/force; acceleration is constant in it, mass is conserved in it and there will be changes in velocities of objects in the closed system.

This question actually seeks to test our knowledge of the law of momentum. The law of conservation of momentum states that the momentum of a closed system is conserved.

answer; /// i believe that the correct answer is (c)

answer: at 24 february, 2014 the population gets twice of its initial population.

explanation:

since we have given that

the population for alpha city, t years after january 1, 2004 is given as

first we find out the initial population, i.e. t=0,

so, our quadratic equation becomes,

according to question, we have said that if the population has twice its initial population, then it becomes

so, time taken to reach this above mentioned population is given by

now, we know that time can't be negative so, we take t=9.149 years.

hence, at 24 february, 2014 the population gets twice of its initial population.