circular motion

Question 1

Newton’s universal law of gravitation

Answer 1

Every single point mass attracts every other point mass with a force that is proportional to the product of their masses and inversely proportional to their separation.

Question 2

GPE

Answer 2

the energy a body possesses due to its position in a gravitational field
Equal to the work done putting it there from a place with zero PE

Question 3

escape speed

Answer 3

the minimum speed that a body needs to leave the Earth and not come back
For the Earth this is about 11 kms−1

Question 4

what causes the centripetal force for a car on a circular track

Answer 4

the friction between the tyres and the road (so if there’s not enough friction the car will travel in a straight line and will appear to be thrown outwards off the track)

Question 5

A communications satellite is moving at a constant speed in a circular orbit around Earth. At any given instant in time, the resultant force on the satellite is?

Answer 5

equal to the gravitational force on the satellite

Question 6

A car goes round a curve in a road at a constant speed. Explain why, although its speed is constant, it is accelerating

Answer 6

Velocity is a vector so as the direction of the car changes, velocity must change
Acceleration is the rate of change of velocity so if velocity changes the car must accelerate

Question 7

time period

Answer 7

time for one complete revolution

Question 8

Frequency

Answer 8

number of revolutions per second

Question 9

angular frequency

Answer 9

angle in radians swept out by radius per unit time

Question 10

centripetal force

Answer 10

The force towards the centre of a circle causing a body to travel in circular motion
This is not a new type of force but the name given to the resultant force

Question 11

Centripetal acceleration

Answer 11

The acceleration of the body due to the unbalanced force towards the centre

Question 12

gravitational field

Answer 12

the region of space where a mass experiences a force due to its mass

Question 13

gravitational potential (V)

Answer 13

work done per unit mass in taking a small point mass from zero potential to the point in question

Question 14

How can escape speed be found

Answer 14

by considering the change of energy as the body leaves the earth and travels to an infinite distance from it

Question 15

difference between geostationary and GPS satellites

Answer 15

Geostationary satellites orbit the Earth once a day; they are about 6Re away from the earth
GPS satellites are much nearer and orbit more often

Question 16

what’s a small angle?

Answer 16

less than 15*

Question 17

coefficient of friction

Answer 17

ratio of friction force/normal reaction force