Definitions and Laws
Kepler's First Law
What is that planets move in elliptical orbits with the Sun at a focus?
Gravitational Field Strength at Earth's surface
What is 9.8 m s-1?
An expression for the total energy of an orbiting object of mass m about a planet with mass M and orbital radius R.
What is -(GMm/2R)?
If I needed to get from F to g, I would do this.
What is divide by m (the mass of the test object)?
The work done when travelling along a line of equipotential.
What is 0?
Gravitational Field Strength
What is the force per unit mass experienced by a small test mass placed at that point?
The Gravitational Constant G with units
What is 6.67 x 10-11 N m2 kg-2?
A bullet has mass 0.03 kg and is on the surface of a planet of mass 4.0 x 1023 kg and radius 800 km. Determine the kinetic energy needed for the bullet to reach infinity.
What is 1000500 J or 1.00 x 106 J?
If I needed to get from V to E I would do this.
What is multiply by m (the mass of the object)?
The complete graph of gravitational field strength against distance from the centre of a spherical mass.
Ask Jon.
Kepler's Third Law
What is that the square of the orbital period is proportional to the radius of orbit cubed?
The radius of the Earth
What is 6.37 x 106 m?
Two spheres of radius 30 cm are touching. They each are 4500 kg. This is the force of gravity between the two spheres.
What is 0.00375 N in an attractive direction?
If I needed to get from potential energy to force I would do this.
What is take the derivative with respect to r?
What is a geosynchronous orbit?
Gravitational Potential
What is the work done per unit mass to bring a test mass from infinity to a point?
The mass of the Earth
What is 5.97 x 1024 kg?
Two planets of mass 36M and M have centres a distance R apart. What is the distance in terms of R from the centre of the 36M planet such that the gravitational potential energy is a maximum?
What is 6R/7?
The angle between a field line and a line of equipotential.
What is 90 degrees?
The eccentricity of the orbit of Pluto (answers within 0.05 accepted)
What is 0.25?
Escape Speed
What is the minimum speed needed for an unpowered object to be launched at to reach infinity from the surface of a planet?
Average distance from Earth to the Sun
What is 1.5 x 1011 m?
Body Ida has a moon, Dactyl, orbiting it with a period of about 20 hours. The exact orbit of Dactyl is not known, but we can assume that it is a circle with radius of about 90km. This is the mass of Ida.
What is 8.32 x 1016 kg?
If I needed to get the gravitational potential from the gravitational field strength, I would do this.
What is take the integral from infinity to R?
Longitudinal Wave
What is a wave where the particles' displacement is parallel to the direction of energy propagation?