Astro 7N Exam 1 UPDATED ACTUAL
Exam Questions and CORRECT Answers
The force of gravity by the Sun keeps the planet in orbit around it, but how do the planets affect
the sun? - CORRECT ANSWER - They exert an equally strong pull on the sun, causing it
move slightly
Newton's First Law - CORRECT ANSWER - An object at rest stays at rest and an object
in motion stays in motion with the same speed and in the same direction unless acted upon by an
unbalanced force.
ex: if the sun suddenly disappeared, the Earth would continue in the direction that it was
traveling in its orbit at that time
Newton's Second Law - CORRECT ANSWER - The acceleration of a body due to a force
will be in the same direction as the force, with magnitude directly proportional to its mass
Force = mass x acceleration
A smaller mas will move faster, if the same force is applied to it
Newton's Third Law - CORRECT ANSWER - For every action there is an equal and
opposite reaction
The Sun exerts force on planets, and they orbit it - he planets exert equal force on Sun, but it only
moves slightly because of its very large mass relative to the planets
Surface Gravity on a Planet - CORRECT ANSWER - the strength of gravity: g = m/r^2
where M is the mass of the planet and R is its radius. Note the radius is squared but the mass is
not.
,More mass = more gravity.
- If the mass of a planet were twice that of another, but they had the same radius, the gravity felt
on the surface of the more-massive one would be twice as strong.
Larger separation = less gravity.
- If the radius of a planet were twice that of another, the gravity is 1 / (2) 2 = 1/4 as strong.
Putting the effects of mass and radius together, you should be able to figure out the surface
gravity of Mars, relative to the Earth.
- Mars has 1/10 the mass of the Earth and 1/2 the radius of Earth. So for Mars,
g = (1/10) / (1/2) 2 = (1/10) / (1/4) = 4/10
Mars has a surface gravity 4/10 that of Earth. You will need to be able to do this type of estimate
for the test, given the numbers for mass and radius.
If I apply exactly the same amount of force to a pebble and a boulder, what will happen -
CORRECT ANSWER - the pebble will move faster
If the Earth were moved to half its current distance from the sun, how would the force of gravity
by the sun on the earth change? - CORRECT ANSWER - it would become 4 times weaker
Mass - CORRECT ANSWER - As the mass of the planet increases, the jump height does
decreases by the same factor
As the mass of the planet decreases, the jump height does increases by the same factor
According to Newton's Second law of motion, if the net force acting on the object increases
while the mass of the object remains constant, what happens to acceleration - CORRECT
ANSWER - acceleration increases
, If the earth were moves to half its current distance from the Sun, how would the force of gravity
by the Sun on the Earth change - CORRECT ANSWER - it would become four times
weaker
What did newton's law of universal gravitation tell us about how gravity works - CORRECT
ANSWER - the force of gravity from the sun will be stronger on object with more mass
If you were to sit on the ground, there would be a force due to gravity pulling you toward the
earth. which of the following is true according to newton's third law - CORRECT
ANSWER - you are pushing the earth away from yourself with the same force
what would happen to the earth sun's gravity somehow turned off instantaneously - CORRECT
ANSWER - it would continue to move in the line in the same direction it was moving
when the gravity turned off
Newton's Universal Law of Gravitation - CORRECT ANSWER - This law gives the force
of gravity between any two objects in the Universe. The force of gravity is proportional to (mass
of object 1) × (mass of object 2) divided by the distance between the two objects squared:
F M1 x M2 / d 2
Again, more mass = stronger gravity. If the objects were moved 2 times closer (or, to half of
their initial distance between), ...
F M1 x M2 / (1/2) 2 = M1 x M2 / (1/4) = 4 (M1 x M2)
... so, the gravitational attraction would become 4 times as great.
The Seasons, Day & Night - CORRECT ANSWER - Q: What causes day and night?
A: Rotation of the Earth on its axis.
Q: How does the Sun appear to move in the sky in the course of a day?
A: East to West, because of Earth's rotation. The stars and planets move in the same
way from our point of view, also, because of Earth's rotation.
Exam Questions and CORRECT Answers
The force of gravity by the Sun keeps the planet in orbit around it, but how do the planets affect
the sun? - CORRECT ANSWER - They exert an equally strong pull on the sun, causing it
move slightly
Newton's First Law - CORRECT ANSWER - An object at rest stays at rest and an object
in motion stays in motion with the same speed and in the same direction unless acted upon by an
unbalanced force.
ex: if the sun suddenly disappeared, the Earth would continue in the direction that it was
traveling in its orbit at that time
Newton's Second Law - CORRECT ANSWER - The acceleration of a body due to a force
will be in the same direction as the force, with magnitude directly proportional to its mass
Force = mass x acceleration
A smaller mas will move faster, if the same force is applied to it
Newton's Third Law - CORRECT ANSWER - For every action there is an equal and
opposite reaction
The Sun exerts force on planets, and they orbit it - he planets exert equal force on Sun, but it only
moves slightly because of its very large mass relative to the planets
Surface Gravity on a Planet - CORRECT ANSWER - the strength of gravity: g = m/r^2
where M is the mass of the planet and R is its radius. Note the radius is squared but the mass is
not.
,More mass = more gravity.
- If the mass of a planet were twice that of another, but they had the same radius, the gravity felt
on the surface of the more-massive one would be twice as strong.
Larger separation = less gravity.
- If the radius of a planet were twice that of another, the gravity is 1 / (2) 2 = 1/4 as strong.
Putting the effects of mass and radius together, you should be able to figure out the surface
gravity of Mars, relative to the Earth.
- Mars has 1/10 the mass of the Earth and 1/2 the radius of Earth. So for Mars,
g = (1/10) / (1/2) 2 = (1/10) / (1/4) = 4/10
Mars has a surface gravity 4/10 that of Earth. You will need to be able to do this type of estimate
for the test, given the numbers for mass and radius.
If I apply exactly the same amount of force to a pebble and a boulder, what will happen -
CORRECT ANSWER - the pebble will move faster
If the Earth were moved to half its current distance from the sun, how would the force of gravity
by the sun on the earth change? - CORRECT ANSWER - it would become 4 times weaker
Mass - CORRECT ANSWER - As the mass of the planet increases, the jump height does
decreases by the same factor
As the mass of the planet decreases, the jump height does increases by the same factor
According to Newton's Second law of motion, if the net force acting on the object increases
while the mass of the object remains constant, what happens to acceleration - CORRECT
ANSWER - acceleration increases
, If the earth were moves to half its current distance from the Sun, how would the force of gravity
by the Sun on the Earth change - CORRECT ANSWER - it would become four times
weaker
What did newton's law of universal gravitation tell us about how gravity works - CORRECT
ANSWER - the force of gravity from the sun will be stronger on object with more mass
If you were to sit on the ground, there would be a force due to gravity pulling you toward the
earth. which of the following is true according to newton's third law - CORRECT
ANSWER - you are pushing the earth away from yourself with the same force
what would happen to the earth sun's gravity somehow turned off instantaneously - CORRECT
ANSWER - it would continue to move in the line in the same direction it was moving
when the gravity turned off
Newton's Universal Law of Gravitation - CORRECT ANSWER - This law gives the force
of gravity between any two objects in the Universe. The force of gravity is proportional to (mass
of object 1) × (mass of object 2) divided by the distance between the two objects squared:
F M1 x M2 / d 2
Again, more mass = stronger gravity. If the objects were moved 2 times closer (or, to half of
their initial distance between), ...
F M1 x M2 / (1/2) 2 = M1 x M2 / (1/4) = 4 (M1 x M2)
... so, the gravitational attraction would become 4 times as great.
The Seasons, Day & Night - CORRECT ANSWER - Q: What causes day and night?
A: Rotation of the Earth on its axis.
Q: How does the Sun appear to move in the sky in the course of a day?
A: East to West, because of Earth's rotation. The stars and planets move in the same
way from our point of view, also, because of Earth's rotation.
