AP Physics C: Mechanics : Gravity
Study concepts, example questions & explanations for AP Physics C: Mechanics
All AP Physics C: Mechanics Resources
Example Questions
Example Question #1 : Calculating Weight
The force on an object due to gravity on the moon is one-sixth of that found on Earth. What is the acceleration due to gravity on the moon?
We can use Newton's second law:
Set up equations for the force on the moon and the force on Earth:
Now we can use substitution:
From this, we can see that 
Example Question #1 : Calculating Weight
A large planet exerts a gravitational force five times stronger than that experienced on the surface of Earth. What is the weight of a 50kg object on this planet?
The weight of the object on Earth's surface is:
The force on the new planet is five times that on Earth, so we can simply multiply:
Example Question #31 : Forces
A space woman finds herself in an unkown planet with gravity 
We know that the weight of an object is given by:
We know the gravity on the unkown planet, so the weight of the woman is given by:
We need only to find the mass of the woman to solve the problem. Since the mass of the woman is constant, we can use the information about her weight on Earth to figure out her mass.
Use this mass to solve for her weight on the new planet.
Example Question #101 : Mechanics Exam
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 #11 : Gravity
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?
It cannot be determined from the information given
The torque is zero at both a and b
The torque is greater at point a
The torque is greater at point b
The torque is the same at points a and b, but it is not zero
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 #11 : Gravity
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 #1 : Understanding Orbits
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
In the direction of travel
Towards Earth
This maneuver cannot be accomplished
Away from 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.
All AP Physics C: Mechanics Resources
