PHYSICS WS
GRAVITY REVIEW
Conceptual
1.
Since the Earth is constantly attracted to the Sun by the gravitational interaction, why doesn’t it fall into the Sun and burn up?
2.
As a part of their training before going into orbit, astronauts ride in an airliner that is flown along the parabolic trajectory as a
freely falling projectile. Explain why this gives the same apparent weightlessness as being in orbit.
3.
A person has a mass of 75.0 kg. What is their weight on Earth? The travel to planet Daygabba where the value of g is 3 times
what it is on Earth, what is the person’s mass there? What is their weight on Daygabba?
4.
Why is it impractical to put a satellite in orbit at the Earth’s surface? What difficulties are there?
5.
The Earth pulls an apple downward. The Earth is pulled upward by the apple (same force). Why does the apple move and not
the Earth?
6.
What happens to a person’s body if they spend long periods in zero-g?
7.
The diameter of a planet is 5 times that of the Earth’s, yet the acceleration due to gravity on both planets is the same. How is
this possible?
8.
Why can’t you launch a satellite straight up and have it orbit?
9.
State all three of Kepler’s Laws of planetary motion.
10. A planet is traveling in an elliptical orbit. When is it traveling the fastest? The slowest?
11. What is the name for the distance of a elliptical satellite when it is furthest away? When it is closest?
Problems
1.
At what altitude above Earth’s surface would the gravitational acceleration be 4.9 m/s2?
2.
[2.64x106 m]
The Martian satellite Phobos travels in an approximately circular orbit of radius 9.4×10 m with a period of7 hr 39 min.
Calculate the mass of Mars from this information.
3.
[6.47x1023 kg]
The mean distance of Mars from the Sun is 1.52 times that of Earth from the Sun. From Kepler’s law, calculate the number of
years required for Mars to make one revolution around the Sun;
4.
[1.87 yrs]
20 kg satellite has a circular orbit with a period of 2.4 hr and a radius of 8.0 × 106 m around a planet of unknown mass. If the
magnitude of the gravitational acceleration on the surface of the planet is 8.0 m!s 2, what is the radius of the planet?
5.
[5.81x106 m]
A typical GPS (Global Positioning System) satellite orbits at an altitude of 2.0 × 107 m. Find (a) the orbital speed, and (b) the
orbital period of such a satellite
6.
[v = 3890 m/s, T = 42616 sec]
An astronaut exploring a distant solar system lands on an unnamed planet with a radius of 3560 km. When the astronaut
jumps upward with an initial speed of 3.00 m/s, she rises to a height of 0.570 m. What is the mass of the planet?
7.
[1.50x1024 kg]
The asteroid Icarus, though only a few hundred meters across, orbits the Sun like the planets. Its period is 410 d. What is its
average distance from the Sun in meters? In A.U.?
8.
[1.62x1011 m = 1.08 A.U.]
A satellite of mass 5500 kg orbits the Earth and has a period of 6200s. Find (a) the radius, and (b) kinetic energy of the
satellite.
9.
[R = 7.3x106 m, KE = 1.5x1011 J]
How long would a day be (in minutes) if the Earth were rotating so fast that objects at the equator were apparently
weightless? (Hint: Normal force would be zero)
6
[84.5 min]