Answer: 
Explanation:
The equation to calculate the center of mass 
of a particle system is:
In this case we can arrange for one dimension, assuming the geometric center of the Earth and the ladder are on a line, and assuming original center of mass located at the Earth's geometric center:
Where:
is the mass of the Earth
is the mass of 1 billion people
is the radius of the Earth
is the distance between the center of the Earth and the position of the people (2 m above the Earth's surface)
This is the displacement of Earth's center of mass from the original center.
energy never disappears, for example, if you give some kinetic energy to a ball and it stops few seconds later, friction steals this energy to ground which ball was going on. "Law of Conservation of Energy" tell us that energy can't disappear
Answer:
Asteroids are objects made of clay and silicate that orbit the sun but are too small to be considered planets.
Most asteroids revolve around the sun in an orbit between those of Mars and Jupiter.
They form a wide band called the Asteroid belt.
Other asteroids have orbits that cross Earth’s orbit. These asteroids are called Earth-crossers.
Asteroids probably consist of matter that never agglomerated into a planet when the solar system was forming.
The comet’s core is composed of ice and dust.
Comets heat up and begin to change from a solid to a gas as they approach the sun.
The matter surrounding a comet’s core is vaporized and forms a very bright halo of ice or dust not sure, and an enormous cloud of dust or gasses not sure envelopes the head of the comet.
Answer:
t=18s
Explanation:
The final position of an object moving at constant speed is given by the formula 
, where 
is its initial position, v its speed and t the time elapsed.
For the cheetah we have 
, and for the gazelle 
. We want to know at which t their positions are equal, that is, 
, which means,
Where we can do:
We then substitute the values we have (the initial position of the cheetah is 0m), writing the meters in km so distance units cancel out correctly:
On the last step we just multiply by 3600 because is the number of seconds in an hour.
Pressure applied on a system is calculated by dividing the force by the area perpendicular to the direction of the force. It is expressed as:
P = F/A = 1.5 N / 0.5 m^2 = 3 N/m^2
Therefore, the correct answer from the choices is the last option. Hope this answers the question. Have a nice day.
