AP Physics 1 : Universal Gravitation

Study concepts, example questions & explanations for AP Physics 1

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Example Questions

Example Question #82 : Forces

An electronic scale is used to find the mass of a lead cube at sea level. The scale and lead cube are then transported to the top of a mountain, over  above sea level. How does the weight reading compare to the weight given at sea level?

Possible Answers:

It will be larger

It will be smaller

It is impossible to determine

None of these

It will be the same

Correct answer:

It will be smaller

Explanation:

The electronic scale measures based on the normal force the scale provides to the object. This in turn is based on the force of gravity on the object by the earth.

As height above sea level increases, as does , the distance to the center of the Earth. As  increases,  decreases. This would decrease the normal force which would decrease the reading on the scale.

Example Question #82 : Forces

Mass of moon:

Radius of moon:

A spring of rest length is placed upright on the moon. A mass of is gently placed on top and the spring contracts by . Determine the spring constant.

Possible Answers:

None of these

Correct answer:

Explanation:

First, estimate the acceleration due to gravity close to the moon's surface:

Combining equations and solving for the acceleration:

Converting to and pugging in values:

Using

Solving for

Converting to and plugging in values:

(Since the mass is at rest, the acceleration and thus the net force is zero)

Example Question #652 : Newtonian Mechanics

A rope is used to accelerate a mass upwards at . Determine the tension in the rope.

Possible Answers:

None of these

Correct answer:

Explanation:

Using

Combining equations:

Solving for and plugging in values:

Example Question #51 : Universal Gravitation

Mass of Earth:

Universal gravitation constant: 

Radius of earth: 

Determine the magnitude of gravitational force by the earth on a   astronaut above the surface of the earth.

Possible Answers:

Correct answer:

Explanation:

Finding total distance from center of Earth to astronaut:

Converting to meters

Using Universal Gravitation equation:

Plugging in values:

Example Question #52 : Universal Gravitation

Mass of Jupiter:

Universal gravitation constant:

Radius of Jupiter: 

A marble is placed  from the surface of Jupiter. Determine the acceleration due to the gravity of Jupiter.

Possible Answers:

None of these

Correct answer:

Explanation:

Using

and

Combining equations

Solving for

Plugging in values:

Example Question #53 : Universal Gravitation

Mass of Pluto:

Radius of Pluto:

A spring of rest length  is placed upright on Pluto. A mass of  is gently placed on top and the spring contracts by . Determine the spring constant.

Possible Answers:

None of these

Correct answer:

Explanation:

First, estimate the acceleration due to gravity close to Pluto's surface:

Combining equations and solving for the acceleration:

Plugging in values:

Using

Solving for

Converting to and plugging in values:

(Since the mass is at rest, the acceleration and thus the net force is zero)

Example Question #661 : Newtonian Mechanics

Mass of Mars:

Radius of Mars: 

A spring of rest length  is placed upright on Mars. A mass of  is gently placed on top and the spring contracts by . Determine the spring constant.

Possible Answers:

None of these

Correct answer:

Explanation:

First, estimate the acceleration due to gravity close to the martian surface:

Combining equations and solving for the acceleration:

Plugging in values:

Using

Solving for

Converting to and plugging in values:

(Since the mass is at rest, the acceleration and thus the net force is zero)

Example Question #662 : Newtonian Mechanics

Determine the surface gravitational constant for a roughly spherical asteroid of mass  and a radius of 

Possible Answers:

None of these

Correct answer:

Explanation:

Setting universal gravitation equal to the surface gravitational approximation

Where  will be the surface gravitational acceleration constant

Solving for 

Plugging in values

Example Question #701 : Ap Physics 1

Determine the surface gravitational constant for a roughly spherical asteroid of mass  and a radius of .

Possible Answers:

None of these

Correct answer:

Explanation:

Setting universal gravitation equal to the gravitational approximation

Where  will be the surface gravitational acceleration constant

Solving for 

Converting  to  and plugging in values

Example Question #664 : Newtonian Mechanics

Astronauts have recently detected a new exoplanet, Zina. The mass of the planet is twice that of Earth, and the radius is three times larger than Earth's radius. What fraction of our gravity is experienced on this planet?

Possible Answers:

Same gravity because gravity is constant.

Correct answer:

Explanation:

The gravity equation is:

, where  is the universal gravitation constant,  is the mass of the planet, and   is the radius of planet. To find a ratio between the gravity on the planet Zina and our planet, we need to plug in the relevant information:

Remember, we are doing a ratio, so if we reference everything in terms of Earth numbers, the bottom fraction becomes much simpler and cancels out with the top fraction. Also, the gravitational constant is constant, so it cancels out. Therefore, the only important information are the ratios the mass and radius differ from Earth's. 

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