Define gravitational potential .

Gravitational potential is the work done per unit mass in bringing a mass from infinity to a defined point in the field.

Why is gravitational potential always negative everywhere except at infinity?

Gravity is attractive , so work must be done on a mass to move it to infinity, where potential is defined as zero . Since potential energy increases as a mass moves towards infinity, the potential everywhere else must be negative .

Which equation gives gravitational potential energy (G.P.E) near the Earth's surface, and what is assumed about the G.P.E at the surface?

G.P.E = mg Δ*h ; the G.P.E at the Earth's surface is taken to be zero *.

Near the Earth's surface, the gravitational field is approximated to be .......... , but far away it is radial because the Earth is a sphere.

Near the Earth's surface, the gravitational field is approximated to be uniform , but far away it is radial because the Earth is a sphere.

True or False? Gravitational potential decreases as an object moves away from a planet, towards infinity.

False. Gravitational potential increases (becomes less negative) as an object moves away from a planet, reaching zero at infinity.

How does gravitational potential vary with distance r from a mass M ?

Gravitational potential is inversely proportional to r ( V g ∝ −1/ r ); it increases (becomes less negative) as r increases.

Define gravitational potential difference , Δ V .

The difference between the final and initial gravitational potential: Δ V = V f − V i .

Gravitational potential and gravitational field strength are both measured from the .......... of the mass causing the field.

Gravitational potential and gravitational field strength are both measured from the centre of the mass causing the field.

True or False? Gravitational potential is proportional to 1/ r 2 , the same as gravitational field strength.

False. Gravitational potential is proportional to 1/*r , whereas gravitational field strength is proportional to 1/ r 2 *.

What is the shape of a force-distance graph for a point or spherical mass, and why?

A curve , because force is inversely proportional to r 2 ( F ∝ 1/ r 2 ).

What does the area under a force-distance graph represent?

The work done (energy transferred), which is the change in gravitational potential energy .

Why is work done on a satellite of mass m when it moves further away from a mass M ?

Gravity is attractive , so energy must be transferred to work against the gravitational force as the satellite moves away.

The gravitational force between two masses is inversely proportional to the .......... of the distance between them.

The gravitational force between two masses is inversely proportional to the square of the distance between them.

True or False? On a force-distance graph, force is directly proportional to distance.

False. Force is inversely proportional to the square of the distance ( F ∝ 1/ r 2 ), so the graph is a curve, not a straight line.

Define gravitational potential energy .

The energy a mass possesses due to its position in a gravitational field, equal to its mass multiplied by the gravitational potential at that point: E = mV g .

Why is work done when a mass moves away from a planet within its gravitational field?

Gravity is attractive , so energy must be transferred to work against the field as the mass moves against the field lines.

The equation Δ G.P.E = mg Δ h can only be used for objects near the Earth's surface, where the gravitational field is approximately .......... .

The equation Δ G.P.E = mg Δ h can only be used for objects near the Earth's surface, where the gravitational field is approximately uniform .

True or False? The equation ΔG.P.E = mg Δ h can be used to find the change in gravitational potential energy of a satellite far from the Earth's surface.

False. That equation only applies in the uniform field near the Earth's surface. Far away, g is no longer constant, so the change in G.P.E must be found using GMm (1/ r 1 − 1/ r 2 ) instead.

Define escape velocity .

The minimum speed that allows an object to escape a gravitational field with no further energy input .

Why is escape velocity the same for all masses in a given gravitational field?

Escape velocity is found by equating kinetic energy to gravitational potential energy, ½ mv 2 = GMm / r . The mass m of the escaping object cancels from both sides, so v does not depend on m .

Rockets launched from the Earth's surface do not need to reach escape velocity because they are given energy .......... through fuel to provide thrust.

Rockets launched from the Earth's surface do not need to reach escape velocity because they are given energy continuously through fuel to provide thrust.

True or False? Escape velocity is the speed needed to travel far enough from a planet's surface to be considered clear of the planet.

False. Escape velocity is the speed needed to escape the planet's gravitational field altogether, not just its surface. This can require travelling a large distance beyond the surface.

A LevelPhysicsOCRFlashcards5. Newtonian World & AstrophysicsGravitational Potential & Energy

Gravitational Potential & Energy (OCR A Level Physics): Flashcards

Exam code: H556

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FrontGravitational Potential
Define gravitational potential.

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Cards in this collection (30)

Define gravitational potential.
Gravitational potential is the work done per unit mass in bringing a mass from infinity to a defined point in the field.
Where is gravitational potential defined to be zero?
At infinity.
Why is gravitational potential always negative everywhere except at infinity?
Gravity is attractive, so work must be done on a mass to move it to infinity, where potential is defined as zero. Since potential energy increases as a mass moves towards infinity, the potential everywhere else must be negative.
Which equation gives gravitational potential energy (G.P.E) near the Earth's surface, and what is assumed about the G.P.E at the surface?
G.P.E = mgΔ*h; the G.P.E at the Earth's surface is taken to be zero*.
Near the Earth's surface, the gravitational field is approximated to be .........., but far away it is radial because the Earth is a sphere.
Near the Earth's surface, the gravitational field is approximated to be uniform, but far away it is radial because the Earth is a sphere.
True or False?
Gravitational potential decreases as an object moves away from a planet, towards infinity.
False.
Gravitational potential increases (becomes less negative) as an object moves away from a planet, reaching zero at infinity.
State the equation for gravitational potential V_g at distance r from a point mass M.
$V_{g} = - \frac{G M}{r}$
How does gravitational potential vary with distance r from a mass M?
Gravitational potential is inversely proportional to r (V_g ∝ −1/r); it increases (becomes less negative) as r increases.
Define gravitational potential difference, ΔV.
The difference between the final and initial gravitational potential: ΔV = V_f − V_i.
Give the equation for the change in gravitational potential between two points at distances r₁ and r₂ from mass M.
$Δ V = G M (\frac{1}{r_{1}} - \frac{1}{r_{2}})$
Gravitational potential and gravitational field strength are both measured from the .......... of the mass causing the field.
Gravitational potential and gravitational field strength are both measured from the centre of the mass causing the field.
True or False?
Gravitational potential is proportional to 1/r², the same as gravitational field strength.
False.
Gravitational potential is proportional to 1/*r, whereas gravitational field strength is proportional to 1/r²*.
Define Newton's Law of Gravitation.
The force F between two masses M and m separated by distance r is given by $F = \frac{G M m}{r^{2}}$
What is the shape of a force-distance graph for a point or spherical mass, and why?
A curve, because force is inversely proportional to r² (F ∝ 1/r²).
What does the area under a force-distance graph represent?
The work done (energy transferred), which is the change in gravitational potential energy.
Why is work done on a satellite of mass m when it moves further away from a mass M?
Gravity is attractive, so energy must be transferred to work against the gravitational force as the satellite moves away.
The gravitational force between two masses is inversely proportional to the .......... of the distance between them.
The gravitational force between two masses is inversely proportional to the square of the distance between them.
True or False?
On a force-distance graph, force is directly proportional to distance.
False.
Force is inversely proportional to the square of the distance (F ∝ 1/r²), so the graph is a curve, not a straight line.
Define gravitational potential energy.
The energy a mass possesses due to its position in a gravitational field, equal to its mass multiplied by the gravitational potential at that point: E = mV_g.
Give the equation for gravitational potential energy E between two masses M and m separated by distance r.
$E = - \frac{G M m}{r}$
Give the equation linking work done ΔW, mass m, and change in gravitational potential ΔV.
$Δ W = m Δ V$
Why is work done when a mass moves away from a planet within its gravitational field?
Gravity is attractive, so energy must be transferred to work against the field as the mass moves against the field lines.
The equation ΔG.P.E = mgΔh can only be used for objects near the Earth's surface, where the gravitational field is approximately ...........
The equation ΔG.P.E = mgΔh can only be used for objects near the Earth's surface, where the gravitational field is approximately uniform.
True or False?
The equation ΔG.P.E = mgΔh can be used to find the change in gravitational potential energy of a satellite far from the Earth's surface.
False.
That equation only applies in the uniform field near the Earth's surface. Far away, g is no longer constant, so the change in G.P.E must be found using GMm(1/r₁ − 1/r₂) instead.
Define escape velocity.
The minimum speed that allows an object to escape a gravitational field with no further energy input.
What two properties of a body determine its escape velocity?
Its mass and radius.
Give the equation for escape velocity v at the surface of a mass M of radius r.
$v = \sqrt{\frac{2 G M}{r}}$
Why is escape velocity the same for all masses in a given gravitational field?
Escape velocity is found by equating kinetic energy to gravitational potential energy, ½mv² = GMm/r. The mass m of the escaping object cancels from both sides, so v does not depend on m.
Rockets launched from the Earth's surface do not need to reach escape velocity because they are given energy .......... through fuel to provide thrust.
Rockets launched from the Earth's surface do not need to reach escape velocity because they are given energy continuously through fuel to provide thrust.
True or False?
Escape velocity is the speed needed to travel far enough from a planet's surface to be considered clear of the planet.
False.
Escape velocity is the speed needed to escape the planet's gravitational field altogether, not just its surface. This can require travelling a large distance beyond the surface.

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