Gravitational Field

Question 1

Why is GPE negative?

Answer 1

GPE taken to be zero at infinity. As gravitational force is attractive, work done by external force in moving mass from infinity is negative

Question 2

What is the range of values of R for expressions to be valid?

Answer 2

Greater than or equal to the radius of the source

Question 3

Define Gravitational Field Strength.

Answer 3

Gravitational force per unit mass acting on a small mass placed in a gravitational field

Question 4

Define Gravitational Field.

Answer 4

Region of space where a mass experiences a force

Question 5

Define Gravitational Potential Energy.

Answer 5

Work done by external force on a mass to move it from infinity to a point

Question 6

Define Gravitational Potential.

Answer 6

Work done per unit mass by external force on a point mass to move it from infinity to a point

Question 7

Formula for Gravitational Force, F, scalar or vector?

Answer 7

GMm/r^2 , Vector

Question 8

Formula for Gravitational Field Strength, g, scalar or vector?

Answer 8

GM/r^2 , gr^2=GM , Vector

Question 9

Formula for Gravitational Potential Energy, U, scalar or vector?

Answer 9

-GMm/r , Scalar

Question 10

Formula for Gravitational Potential, o/, scalar or vector?

Answer 10

-GM/r , Scalar

Question 11

Relationship between Gravitational force (F) and Gravitational Field Strength (g)

Answer 11

F=mg

Question 12

Relationship between Gravitaional Potential Energy (U) and Gravitational Potential (o/)

Answer 12

U=mo

Question 13

What is equipotential? + ___________

Answer 13

Points same distance from source have same gravitaional potential + No work done along same equipotential

Question 14

Relationship between Gravitational force (F) and Gravitaional Potential Energy (U)

Answer 14

F = -dU/dr

Question 15

Relationship between Gravitational Field Strength (g) and Gravitational Potential (o/)

Answer 15

g = -do/dr

Question 16

How to derrive escape speed formula?

Answer 16

Final KE and GPE equal zero

Question 17

What can be found from GMm/r^2 = mv^2/r?

Answer 17

Linear velocity and kinetic energy

Question 18

What can be found from GMm/r^2 = mrw^2? State the relationship between the two quantities.

Answer 18

Angular velocity and period, T=2pi/w

Question 19

Why are geostationary satellites placed vertically above equator?

Answer 19

Force of attration to Earth is to its centre so circular orbit must be centred on Earth’s centre. Make sure satellite does not have varying latitude.

Question 20

Where does True weight and Apparent weight occur?

Answer 20

Poles, Equator