Gravitational and Circular Motion

Question 1

Definition of Newton’s Law of Gravitation

Answer 1

-force proportional to product of masses
-force inversely proportional to square of separation

Question 2

What is meant by a gravitational force, Fg

Answer 2

-force acting between 2 masses
or
-force on mass due to gravitational field
or
-force on mass in gravitational field

Question 3

Define gravitational field strength, g

Answer 3

gravitational force per unit mass

Question 4

Define gravitational potential, Ep

Answer 4

work done in moving/bringing unit mass from infinity to the point

Question 5

Why values of gravitational potential near an isolated mass are all negative?

Answer 5

-potential at infinity defined as zero
-forces are always attractive
so work got out ( or done by system ) in moving object to point

Question 6

What is meant by angular velocity?

Answer 6

-rate of change of angle / angular displacement
-swept out by radius

Question 7

What is meant by a field of force?

Answer 7

region (of space) where a particle/body experiences a force

Question 8

What is meant by a gravitational field?

Answer 8

region of space where a mass experiences a force

Question 9

Define radian

Answer 9

-angle (subtended) at the centre of circle
-by an arc equal in length to the radius (of the circle)

Question 10

What is meant by angular speed?

Answer 10

-angle swept out per unit time / rate of change of angle
-by the radius

Question 11

Similarities of definitions in Electric potential & Gravitational Potential

Answer 11

-ratio of work done to mass/charge
-work done moving unit mass/charge from infinity
-both have zero potential at infinity

Question 12

Why values of Gravitational potential always negative?
but Electric potential may be positive or negative

Answer 12

-gravitational forces are always attractive ; electric forces can be attractive or repulsive
-gravitational: work got out as masses come together/mass moves from infinity
-electric: work done on charges if same sign, work got out if opposite sign as charges come together

Question 13

Explain how a satellite may be in a circular orbit around a planet

Answer 13

-gravitational force of attraction between satellite and a planet
provides centripetal force on satellite about the planet

Question 14

Explain why the orbital path of the moon is circular

Answer 14

-gravitational force provides the centripetal force
-force has constant magnitude (centripetal/gravitational)
-force is perpendicular to velocity of moon/ direction of motion of moon

Question 15

What is angular displacement θ ?

Answer 15

angle turned through by an object in any direction in radian

Question 16

3 common ways to find angular speed ω

Answer 16

ω = v/r
=2𝜋/T
=2𝜋f

Question 17

How to calculate centripetal force, Fc

Answer 17

Fc= mrω²
=mv²/r