AP Physics C: Mechanics : Understanding Orbits
Study concepts, example questions & explanations for AP Physics C: Mechanics
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Example Questions
Example Question #1 : Understanding Orbits
If 
Not enough information
Escape velocity is the velocity at which the kinetic energy of an object in motion is equal in magnitude to the gravitational potential energy. This allows us to set two equations equal to each other: the equation for kinetic energy of an object in motion and the equation for gravitational potential energy. Therefore:
In this case, 
Since the radius of the new planet is 
Where 
Example Question #1 : Understanding Orbits
A comet is in an elliptical orbit about the Sun, as diagrammed below:
The mass of the comet is very small compared to the mass of the Sun.
In the diagram above, how does the net torque on the comet due to the Sun's gravitational force compare at the two marked points?
The torque is greater at point b
The torque is zero at both a and b
It cannot be determined from the information given
The torque is the same at points a and b, but it is not zero
The torque is greater at point a
The torque is zero at both a and b
Since the direction of the gravitational force is directly towards the center of the Sun, it lies in the plane of the comet's orbit. Since torque is 
Example Question #3 : Understanding Orbits
A satellite of mass 
Since the gravitational force cannot exert torque on the satellite about the Earth's center, angular momentum is conserved in this orbit:
Example Question #111 : Mechanics Exam
A satellite is in an elliptical orbit about the Earth. If the satellite needs to enter a circular orbit at the apogee of the ellipse, in what direction will it need to accelerate?
Opposite the direction of travel
Away from Earth
In the direction of travel
This maneuver cannot be accomplished
Towards Earth
In the direction of travel
Since the speed of the satellite at apogee is too low for a circular orbit at that orbital radius, the satellite needs to speed up to circularize the orbit.
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