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Gravitation
Created by Craig Smiley (Harrison HS, West Lafayette, IN)
Supported by grant PHY-0851826
from the National Science Foundation
and by Purdue University
Gravitation
If you used a rocket pack to fly to a height equal to
Mars’ radius above the surface of Mars, what would
happen to your weight? (ignore the weight of the
rocket pack)
A. Decrease to a 1/4 of your weight
B. Decrease to a 1/2 of your weight
C. Stay the same
D. Increase by 2x your weight
E. Increase by 4x your weight
F. You would be weightless
Orbits
What would need to happen to maintain Earth’s circular
orbit around the Sun if the Earth’s mass suddenly
increased?
A. Increase Earth’s radius
B. Increase Earth’s orbiting speed
C. Increase Sun’s mass
D. Decrease the distance between Earth and Sun
E. Nothing would have to change
Orbits
What would need to happen to the Earth to maintain a
circular orbit if Sun’s mass decreased?
A. Distance from Sun ↑ or Earth’s speed ↑
B. Distance from Sun ↑ or Earth’s speed ↓
C. Distance from Sun ↓ or Earth’s speed ↑
D. Distance from Sun ↓ or Earth’s speed ↓
E. None of these
Orbits
Assuming all the planets have circular orbits around the
Sun, what happens to the planets’ period of revolution
(time around the Sun) as you get farther away from the
sun
A. Get shorter
B. Get longer
C. Stay the same
D. Can’t be determined without the mass of the planet
Orbits
Assuming all the planets have circular orbits around the
Sun, what happens to the planets’ period of revolution
(time around the Sun) as you get farther away from the
sun
A. Get shorter
B. Get longer
C. Stay the same
D. Can’t be determined without the mass of the planet
Circular Orbits
What would need to happen to maintain Earth’s circular
orbit around the Sun if the Earth’s mass suddenly
increased?
A. Increase Earth’s radius
B. Increase Earth’s orbiting speed
C. Increase Sun’s mass
D. Decrease the distance between Earth and Sun
E. Nothing would have to change
Circular Orbits
The Sun’s mass doubled. What would need to happen to
the Earth’s distance from the center of the Sun to
maintain a circular orbit moving at its original speed?
A. 4r
B. 2r
C.
2r
D.
r
2
E.
F.
r
4
r
2
Circular Orbits
The Sun’s mass is halved. What would need to happen
to the Earth’s speed to maintain a circular orbit moving
at its original distance from the center of the Sun ?
A. 4v
B. 2v
C.
2v
D.
v
2
E.
F.
v
4
v
2
Suppose the Sun were to collapse into a black hole
(shrinks radius, but maintains the same mass). What
effect would this have on the Earth’s orbit?
A. The size of the orbit would decrease and the
orbital period would decrease.
B. The size of the orbit would increase and the
orbital period would increase.
C. The size of the orbit and the orbital period
would remain unchanged.
D. none of these
Circular Orbits
Assuming all the planets have circular orbits around the
Sun, what happens to the planets’ period of revolution
(time around the Sun) as you get farther away from the
sun
A. Get shorter
B. Get longer
C. Stay the same
D. Can’t be determined without the mass of the planet
The planet Saturn has 100 times the mass of the Earth and
is 10 times more distant from the Sun than the Earth is
(assume it also has a circular orbit).
Compared to the Earth’s acceleration as it orbits the Sun,
the acceleration of Saturn as it orbits the Sun is
A. 100 times greater.
B. 10 times greater.
C. the same.
D. 1/10 as great.
E. 1/100 as great.
Apparent Weight
While the space-shuttle orbits the Earth the astronauts
appear to be weightless:
A. There is no gravity above the atmosphere
B. The force of gravity is much weaker when they are
that far away from the Earth
C. They are constantly “falling” around the Earth
D. None of these
Apparent Weight
Show Vomit Comet Video http://www.youtube.com/watch?v=BTkFIE_-kL8
Why were they floating inside the plane?
A. They went high enough so there was very little
gravity acting on them.
B. The plane was accelerating downward at 9.8m/s2 so
they were “falling” while inside the plane.
C. They had powerful magnets in the plane, but in
order for them to work they needed to be off the
ground.
D. None of these.
An astronaut is floating around in the
space shuttle's cabin. What is her
acceleration, as measured from the
earth's surface?
A. zero - she's floating
B. very small, directed towards the center of the earth
C. very small, directed along the line of travel of the shuttle
D. quite large, nearly g, directed towards the center of the
earth
E. quite large, nearly g, directed along the line of travel of
the shuttle
Gravitational Potential Energy
A satellite is moving around the Earth in a circular orbit.
Over the course of an orbit, the Earth’s gravitational force
A. does positive work on the satellite.
B. does negative work on the satellite.
C. does positive work on the satellite during part of the orbit
and negative work on the satellite during the other part.
D. does zero work on the satellite at all points in the orbit.
Dropping a rock from r = ∞
If there was nothing else in the universe except the Earth and a rock,
and the rock was taken to r = ∞ away and released from rest, how fast
would it be going by the time it fell that far before hitting the Earth?
A. Infinitely fast
B. Speed of light, b/c nothing that go faster than the speed of light
C. A little slower than the speed of light because it has mass
D. Significantly slower than the speed of light
Gravitational Equipotential Lines
What happens to gravitational potential energy if you move an object with
mass from a lower value equipotential line to a higher value equipotential line?
A. increases
B. decreases
C. stays the same
height (m)
above
ground zero
60m
600 J/kg
50m
500 J/kg
40m
400 J/kg
30m
300 J/kg
20m
200 J/kg
10m
100 J/kg
0m
0 J/kg
gravitational
potential
(g = 10m/s2)
Gravitational Equipotential Lines
What is the sign for Work done by gravity if you move an object with mass
from a lower value equipotential line to a higher value equipotential line?
A. +
B. –
C. 0
height (m)
above
ground zero
60m
600 J/kg
50m
500 J/kg
40m
400 J/kg
30m
300 J/kg
20m
200 J/kg
10m
100 J/kg
0m
0 J/kg
gravitational
potential
(g = 10m/s2)
Gravitational Equipotential Lines
What is the sign for Work done by gravity if you move an object with mass
from a lower value equipotential line to a higher value equipotential line
and then back to the initial lower value equipotential line?
A. +
B. –
600 J/kg
C. 0 60m
height (m)
above
ground zero
50m
500 J/kg
40m
400 J/kg
30m
300 J/kg
20m
200 J/kg
10m
100 J/kg
0m
0 J/kg
gravitational
potential
(g = 10m/s2)
Gravitational Equipotential Lines
What is the sign for Work done by
gravity if you move an object with
mass around an equipotential line?
A. +
B. –
C. 0
Gravitational Equipotential Lines
What happens to gravitational potential
energy if you move an object with mass
from a lower value equipotential line to
a higher value equipotential line?
A. increases
B. decreases
C. stays the same
Gravitational Equipotential Lines
What is the sign for Work done by
gravity if you move an object with
mass from a lower value
equipotential line to a higher value
equipotential line?
A. +
B. –
C. 0
Gravitational Equipotential Lines
What is the sign for Work done
by gravity if you move an object
with mass from a lower value
equipotential line to a higher
value equipotential line and then
back to the initial lower value
equipotential line?
A. +
B. –
C. 0