7. Gravitational Field

Question 1

What is newton’s law of gravity?

Answer 1

Newtons law of gravity states that the mutual force of attraction between any two point masses is proportional to the product of the masses and inversely proportional to the square of their separation

Question 2

What is the formula of newtons law of gravity?

Answer 2

F=GMm/r²

Question 3

What is a gravitational field?

Answer 3

Gravitational field is a region of space where a mass experiences a force.

Question 4

What is the direction of the gravitational field?

Answer 4

The direction of the field is the direction of the force on the mass

Question 5

What is gravitational field strength?

Answer 5

The gravitational field strength is defined as the gravitational force acting per unit mass on a small unit mass at a point in a gravitational field.

Question 6

What is the formula of gravitational field strength?

Answer 6

g=F/m

Question 7

What is inverse square law field?

Answer 7

When the distance from the centre of the mass increases, the gravitational field at that point decreases. g is proportional to 1/r2

Question 8

When is inverse square law field valid?

Answer 8

It is only valid if the distance from the centre of the mass is larger than the radius of the mass

Question 9

What is gravitational potential energy?

Answer 9

Gravitational potential energy of a mass at a point is the work done on the mass by an external force to move it from infinity to that point

Question 10

What is the equation of gravitational potential energy?

Answer 10

U= -GMm/r

Question 11

Why is gravitational potential energy negative?

Answer 11

Gravitational potential energy at zero is negative because, by convention, gravitational potential energy is taken to be 0 at infinity. Since all gravitational forces are attractive, work done by external force on the mass in moving it from infinity is negative.

Question 12

What is gravitational potential?

Answer 12

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

Question 13

What is the equation of gravitational potential?

Answer 13

𝟇= U/m, -GM/r

Question 14

What is the relation of the distance from the centre of the mass and the gravitational potential?

Answer 14

The gravitational potential increases as the distance from the centre of mass increases

Question 15

What is the gravitational potential at infinity?

Answer 15

the gravitational potential at infinity is 0.

Question 16

Why is gravitational potential negative?

Answer 16

Gravitational potential is negative because, gravitational potential is taken to be zero at infinity and gravitational forces are attractive, work done by external agent on point mass moving from infinity to that point is zero.

Question 17

Does mass affect gravitational potential at a point?

Answer 17

No. it does not depend on the mass at the point
(the m cancels out)

Question 18

How are gravitational force and gravitational potential related?

Answer 18

F= -dU/dr

Question 19

How are gravitational potential and gravitational field strength related?

Answer 19

g= -d𝟇/dr

Question 20

What is escape speed?

Answer 20

escape speed is the minimum speed required to project a mass from the surface of the planet such that it would come to rest at infinity

Question 21

How do satellites orbit around the planet?

Answer 21

the gravitational force by the planet on the satellite provides centripetal force necessary for the satellite’s circular motion

Question 22

What is a geostationary satellite?

Answer 22

Geostationary satellites are satellites which always remain directly above the same spot on earth

Question 23

What is the period of a geostationary satellite?

Answer 23

24 hours

Question 24

What is one advantage and one disadvantage of geostationary satellites?

Answer 24

One advantage: Since they are positioned at high altitudes, they can view the whole earth disk below them, rather than a small area very frequently.
One disadvantage: high altitudes means spatial resolution of their images tend to be poorer than some low orbit polar satellites.

Question 25

What is true weight and apparent weight?

Answer 25

True weight: gravitational force acting on a mass in a gravitational field
Apparent weight: perceived weight due to addition force from centripetal acceleration

Question 26

What is true weightlessness and weightlessness?

Answer 26

True weightlessness is when g=0N/kg
Apparent weightlessness is when person experiences free fall and has zero contact force on him, occurs when weight is the only force acting on a body.