Force of Gravity
Pioneers of Astronomy
Kepler's Laws
Conceptual Questions
Conceptual questions - 2
100
A planet has a mass of 2.6 x 1024 kg and another has a mass of 9.17 x 1022 kg. Calculate the force of gravity if the distance between the planets is 6.35 x 108 m.
3.94 x 1019 N
100
Which has more mass, a kilogram of feathers or a kilogram of iron?
A 10-kg brick and a 1-kg book are dropped in a vacuum. The force of gravity on the 10-kg brick is (greater than, less than, or same) than the 1-kg brick?
SAME both 1 kg
The force of gravity is the SAME 9.8 m/s^2 accelerating both objects to the surface
100
You have two stars of roughly the same size at 4.70 x 10^30 kg orbiting each other with a semi major axis of 5.40 x 10^12 m. What is the orbital period of these two stars?
3.15 x 10^9 seconds
100
After a cannonball is fired into frictionless space, the amount of force needed to keep it going equals
a. zero, since no force is necessary to keep it moving.
b. twice the force with which it was fired.
c. one half the force with which it was fired.
d. the same amount of force with which it was fired.
e. one quarter the force with which it was fired
a. zero, since no force is necessary to keep it moving.
100
Name two ways to increase force due to gravity on the surface of a planet.
Decrease radius/distance to center or increase mass of the planet.
200
Two planets are 2.41 x 109 m apart and have identical masses of 8.41 x 1025 kg. What is the force of gravity between the two planets?
8.12 x 1022 N
200
What model did Copernicus have for his model of the solar system? Draw a picture to show this model.
Heliocentric model... Drawing is of sun in the center of the solar system
200
1st Law: Planets move in ____________________ with the Sun at one focus of the ellipse
2nd Law: The orbital _______________________ of a planet varies so that a line joining the Sun and the planet will sweep over equal _______________________ in equal time intervals
3rd Law: The amount of _____________________ a planet takes to orbit the Sun, P, is related to its orbit’s size, a
Ellipse
speed, area
time
200
Increasing this variable will decrease force of gravity.
Distance
200
Two moons orbiting a planet have the same mass, but one is twice as far as the other. Which moon experiences a greater force of gravity from the planet?
The moon that is closer to the planet.
300
The force of gravity from a planet acting on an asteroid is 4.79 x 1012 N. If the asteroid has a mass of 8.21 x 1012 kg and the planet has a mass of 9.34 x 1020 kg, calculate the distance between the asteroid and the planet.
3.268 x 105 m = 326786 m
300
Draw an example of what retrograde motion would look like in the night sky. Use arrows to show which way the planet appears to be moving.
300
In the equation P2 = a3 ,what does the P represent? units?
n the equation P2 = a3 ,what does the a represent? units?
P = period of time to orbit (years)
A = semi-major axis, distance from sun (AU)
300
Solve the Fg equation for r. (get r by itself)
r = sqrt(G*m1*m2/Fg)
300
A planet orbits a star and travels from point A to point B, traveling twice the speed as it travels from point C to point D. Which segment is the planet located CLOSEST to the star on it's orbit?
Segment A to B.
400
The force of gravity on a brick on Earth is 14 N. The mass of the Earth doubles. What is the new force of gravity on the brick if the radius of the Earth does not change?
28 N
400
How did Galileo end up under house arrest? Who put him on house arrest?
Catholic church put him on house arrest FOR LIFE for going against current religion and culture of the times.
400
Use the equation P2 = a3 to solve: Pluto is observed orbiting the Sun at a semimajor axis = 39.25 AU. How long is the planet’s orbit in years? (show math below):
245.9 years to orbit
400
What is the weight of a 6kg pizza with the experiencing the g = 9.8 m/s^2 here on Earth?
58.8 N
400
The Earth has an orbital period of 52 weeks and an orbital radius of 1 AU. Earth's moon has an orbital period of about 4 weeks. Can we solve for the orbital radius of the moon with this information?
No. The moon is not orbiting the same object as the Earth.
500
The force of gravity on a dog is 40 Newtons when it is on the surface of the Earth. What would the new force of gravity be if the radius of the Earth shrunk by one half? (r is divided by two)
160 N
500
What was Eudoxus’s idea for the structure of the night sky?
First scientist to create geocentric model of the solar system. "Bowls within bowls"
500
Use the equation P2 = a3 to solve: A comet is observed orbiting the Sun with a period of 651 years. How far is the comet’s semimajor axis (distance from the sun) in AU? (show math below):
75.11 AU
500
Solve the force of gravity equation for m1 if both planets have different masses.
m1=Fg*r2/(G*m2)
500
One planet orbits a star. Another planet with the same mass orbits the same star, but has twice orbital radius. If the planets are the same size, which has the greatest acceleration due to gravity on the surface.
They have the same acceleration due to gravity on the surface.