Lesson 3.7.2.3
3.7.2.3 Gravitational potential Quiz: AQA Physics, Unit 7
20 questions
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Lesson 3.7.2.3, Gravitational potential: 20 multiple choice questions for the AQA Physics (7408), Unit 7: Fields and their consequences (A-level only), written with Revision Ninja.
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The 20 questions
-
Gravitational potential at a point is defined as:
- the force per unit distance at that point
- the work done per unit mass in lifting a mass from the surface
- the work done per unit mass in bringing a small test mass from infinity to that point
- the energy per unit volume at that point
-
The gravitational potential is taken to be zero:
- at the centre of the planet
- at infinity
- at the Earth's surface
- infinitely far below the surface
-
The gravitational potential in a radial field at distance r from mass M is:
- V = -GM / r
- V = -GM r
- V = GM / r
- V = -GM / r^2
-
The negative sign in V = -GM/r shows that:
- the gravitational field is repulsive
- the mass M is negative
- the potential is positive everywhere
- potential near a mass is lower than at infinity, so work must be done to move a mass away
-
The work done in moving a mass m through a potential difference delta V is:
- delta W = delta V / m
- delta W = m delta V
- delta W = m^2 delta V
- delta W = m delta V^2
-
No work is done when a mass moves along an equipotential surface because:
- the surface is at infinity
- the mass does not move
- the potential difference is zero, so m delta V = 0
- the force is zero along the surface
-
The relation between gravitational field strength and potential is:
- g = delta V / delta r^2
- g = -delta V / delta r
- g = -delta V delta r
- g = -delta r / delta V
-
Estimate the gravitational potential at Earth's surface (M = 6.0 x 10^24 kg, R = 6.4 x 10^6 m, G = 6.67 x 10^-11).
- about -6.3 x 10^7 J kg^-1
- about 6.3 x 10^7 J kg^-1
- about -9.8 J kg^-1
- about -6.3 x 10^6 J kg^-1
-
Using the surface potential of about -6.3 x 10^7 J kg^-1, how much work is needed to move 1000 kg from the surface to infinity?
- about 6.3 x 10^10 J
- about 6.3 x 10^13 J
- about 6.3 x 10^7 J
- about 9.8 x 10^6 J
-
The gravitational potential at a distance 2R from Earth's centre is:
- about -1.6 x 10^7 J kg^-1
- about -3.1 x 10^7 J kg^-1
- about +3.1 x 10^7 J kg^-1
- about -6.3 x 10^7 J kg^-1
-
On a graph of potential V against distance r from a planet's centre, the gradient equals:
- minus g, the negative of the field strength
- minus GM
- GM
- g
-
A 2.0 kg object is moved from distance 2R to distance R from Earth's centre. What work must an external agent do?
- 6.3 x 10^7 J
- 1.6 x 10^7 J
- 3.1 x 10^7 J
- 1.3 x 10^8 J
-
A mass of 5.0 kg moves through a potential difference of 4.0 J kg^-1. What work is done?
- 9 J
- 0.8 J
- 20 J
- 1.25 J
-
Compared with a point nearer a planet, a point farther from the planet has a gravitational potential that is:
- zero everywhere
- lower, since it is more negative
- higher, since it is less negative
- the same as at the nearer point
-
The equipotential surfaces around a point mass are:
- concentric spheres centred on the mass
- lines radiating from the mass
- ellipses around the mass
- planes parallel to the surface
-
Where is the gravitational potential of a planet most negative?
- midway between the surface and infinity
- at the highest orbit
- at its surface, the closest point to the centre
- at infinity
-
Using the area under a graph of g against r, what is the potential difference between R and 2R for Earth?
- about 9.8 x 10^6 J kg^-1
- about 6.3 x 10^7 J kg^-1
- about 3.1 x 10^7 J kg^-1
- about 1.6 x 10^7 J kg^-1
-
The gravitational potential at the surface of a planet is -5.0 x 10^7 J kg^-1. What energy per unit mass is needed to move a satellite from the surface to infinity?
- 0 J kg^-1
- 1.0 x 10^8 J kg^-1
- 5.0 x 10^7 J kg^-1
- 2.5 x 10^7 J kg^-1
-
A student says gravitational potential is positive near a massive planet because gravity attracts. Which response is best?
- Correct: attraction always gives a positive potential.
- Correct: a positive potential means the field points inwards.
- Incorrect: with zero at infinity, the potential near a mass is negative, since work must be done against gravity to move a mass out to infinity.
- Incorrect: the potential is always zero near a planet's surface.
-
Compare the work needed to move 1.0 kg from R to 2R with the work needed to move it from 2R to 4R, in the same field.
- 1/2
- 4
- 1
- 2
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