Gravitation

A satellite travels around the Earth in a circular orbit. What is true about the forces acting in this situation?

• The resultant force is the same direction as the satellite’s acceleration.

• The gravitational force acting on the satellite is negligible.

• There is no resultant force on the satellite relative to the Earth.

• The satellite does not exert any force on the Earth.

Satellite X orbits a planet with orbital radius R. Satellite Y orbits the same planet with orbital radius 2R. Satellites X and Y have the same mass.
What is the ratio
 $\frac{centripetalacceleration\ of\ X}{centripetalacceleration\ of\ Y}$  ?

•  $\frac{1}{4}$  

•  $\frac{1}{2}$  

•  $2$  

•  $4$  

Which graph shows the relationship between gravitational force F between two point masses and their separation r?

• A

• B

• C

• D

Newton’s law of gravitation

• is equivalent to Newton’s second law of motion.

• explains the origin of gravitation.

• is used to make predictions.

• is not valid in a vacuum.

The gravitational field strength at the surface of Earth is g. Another planet has double the radius of Earth and the same density as Earth. What is the gravitational field strength at the surface of this planet?

• $\frac{g}{2}$

• $\frac{g}{4}$

• $2g$

• $4g$

The centre of the Earth is separated from the centre of the Moon by a distance D. Point P lies on a line joining the centre of the Earth and the centre of the Moon, a distance X from the centre of the Earth. The gravitational field strength at P is zero.
What is the ratio  $\frac{mass\ of\ the\ Moon}{mass\ of\ the\ Earth}$  ?

•  $\frac{\left(D-X\right)^2}{X^2}$  

•  $\frac{\left(D-X\right)^{ }}{X^2}$  

•  $\frac{X^2}{\left(D-X\right)^2}$  

•  $\frac{X^2}{\left(D-X\right)^{ }}$  

On Mars, the gravitational field strength is about  $\frac{1}{4}$  
of that on Earth. The mass of Earth is approximately ten times that of Mars.
What is
 $\frac{radius\ of\ Earth}{radius\ of\ Mars}$  ?

• 0.4

• 0.6

• 1.6

• 2.5

What is the correct definition of gravitational field strength?

• The mass per unit weight

• The weight of a small test mass

• The force acting on a small test mass

• The force per unit mass acting on a small test mass

Which single condition enables Newton’s universal law of gravitation to be used to predict the force between the Earth and the Sun?

• The Earth and the Sun both have a very large radius.

• The distance between the Earth and the Sun is approximately constant.

• The Earth and the Sun both have a very large mass

• The Earth and the Sun behave as point masses.

A planet has half the mass and half the radius of the Earth. What is the gravitational field strength at the surface of the planet? The gravitational field strength at the surface of the Earth is 10 N kg^–1.

• 2.5 N kg^–1

• 5 N kg^–1

• 10 N kg^–1

• 20 N kg^–1