4.2 Out Into Space

Question 1

What is a vector quantity?

Answer 1

Something that has magnitude and direction.

Question 2

Give the equation for momentum.

Answer 2

p = m v

Question 3

What the the units of momentum?

Answer 3

kg m s^-1 (or Ns)

Question 4

Is momentum always conserved?

Answer 4

Yes.

Question 5

What is Newton’s 1st law of motion?

Answer 5

The velocity of an object will not change unless a resultant for acts upon it.

Question 6

What is the resultant force on an object moving at a constant speed?

Answer 6

Zero

Question 7

What is Newton’s 2nd law of motion?

Answer 7

The rate of change of momentum of an object is directly proportional to the results force which acts upon the object.

Question 8

Give the equation for Newton’s 2nd law.

Answer 8

F = ∆mv / ∆t

Question 9

Give the equation for Newton’s 2nd law for when mass does not change.

Answer 9

F = ma

Question 10

What is the resultant force?

Answer 10

The vector sum of all forces acting on an object.

Question 11

What are the units for force?

Answer 11

Newtons, N.

Question 12

What are the units for mass?

Answer 12

Kilograms, kg.

Question 13

If which direction will acceleration occur if there is a resultant force?

Answer 13

In the direction of the resultant force.

Question 14

What is Newton’s 3rd law?

Answer 14

If object A exerts a force on object B, then object B exerts an equal but opposite force on object A.

Question 15

Gravity pulls down on a book whilst a table pushes upward on the book. Why is this not a case of Newton’s 3rd law?

Answer 15

Because the forces are not of the same type. Gravity pulling the Earth up would be an example of Newton’s 3rd law though.

Question 16

Work is done when…

Answer 16

Energy is transferred.

Question 17

Give the equation for work done.

Answer 17

Foce x Distance

Question 18

What are the units for work done?

Answer 18

Joules, J.

Question 19

How could you find work done from a graph?

Answer 19

Find the area under a F vs s graph.

Question 20

W = F s cosθ where θ is…

Answer 20

The angle between the force and the direction of motion.

Question 21

Energy cannot be created or destroyed but it can be…

Answer 21

Transferred from one form to another.

Question 22

Give the equation for efficiency.

Answer 22

Efficiency = useful power output / total power output

Question 23

Name three types of potential energy.

Answer 23

Gravitational, elastic and electrical.

Question 24

Give the equation for gravitational potential energy of objects moving close to the Earth’s surface.

Answer 24

E = m g ∆h

Question 25

Define radians.

Answer 25

The arc-length divided by the radius of the circle.

Question 26

How many radians are in a complete circle?

Answer 26

2π.

Question 27

Convert 45º into radians.

Answer 27

π/4 rad.

Question 28

What is the definition of angular speed?

Answer 28

The angle an object rotates though per second.

Question 29

Give the equation for angular speed, ω.

Answer 29

ω = θ / t

Question 30

Give the equation for linear speed in terms on angular speed.

Answer 30

v = r ω

Question 31

What is the equation for frequency in terms of time period?

Answer 31

f = 1 / T

Question 32

Give the angular speed of an object in terms of frequency (in revolutions per second).

Answer 32

ω = 2 π f

Question 33

A car is travelling at a constant speed in a circular motion. Why is it accelerating?

Answer 33

It's velocity is changing since it's direction is changing and acceleration is rate of change of velocity.

Question 34

Give an equation for radial acceleration in terms of linear speed.

Answer 34

a = v^2 / r

Question 35

Give an equation for centripetal acceleration in terms of angular speed.

Answer 35

a = ω^2 r

Question 36

Give an equation for radial acceleration in terms of angular speed and linear speed.

Answer 36

a = v ω

Question 37

Give two equations for centripetal force.

Answer 37

``` F = mv^2 / r F = m ω^2 r ```

Question 38

Any mass in a gravitational field will experience an...

Answer 38

Attractive force.

Question 39

Force experienced in a gravitational field is always...

Answer 39

Attractive, never repulsive.

Question 40

Gravitational force experience depends on what?

Answer 40

The masses of the two objects and the distance between them.

Question 41

What is a point mass?

Answer 41

Objects that behave as if all their mass is acting at a single point.

Question 42

What is Newton's law of gravitation?

Answer 42

F = -(G M m) / r^2

Question 43

What does r represent in Newton's law of gravitation?

Answer 43

The distance between the centre of the two masses.

Question 44

What is G in Newton's law of gravitation, and what is it's value?

Answer 44

The gravitational constant. 6.67 x 10^-11

Question 45

What are gravitational lines of force (field lines)?

Answer 45

Lines with arrows that show the direction of the force that masses would feel in a gravitational field.

Question 46

If you double the distance between two objects, the gravitational force experienced by the objects will...

Answer 46

Be one quarter of the original value.

Question 47

Descrive a radial field.

Answer 47

A field where the field lines meet at the centre of a mass..

Question 48

What is a uniform field and where might you find one?

Answer 48

A field where the field lines are parallel. At the Earth's surface.

Question 49

What is field strength, g, defined as?

Answer 49

Force per unit mass.

Question 50

What are the units of field strength?

Answer 50

N kg^-1

Question 51

g is a vector quantity. Where does the vector point?

Answer 51

To the centre of the mass of the field being described.

Question 52

Why do you assume g is constant around the surface of the Earth?

Answer 52

Because the field at the surface of the Earth is almost uniform.

Question 53

What is the value of g (acceleration due to gravity) at the Earth's surface?

Answer 53

-9.81 m s^-2 (N kg^-1)

Question 54

What is the gravitational force experienced by an object in a uniform field?

Answer 54

mg

Question 55

The force experienced by a mass in a uniform field is?

Answer 55

Constant.

Question 56

In a uniform gravitational field, potential energy increases with...

Answer 56

Height.

Question 57

What is the equation for change in gravitational potential energy in a uniform gravitational field?

Answer 57

∆PE = m g ∆h

Question 58

In a radial field, g is inversely proportional to...

Answer 58

r^2

Question 59

Give the equation for field strength in a radial field.

Answer 59

g = -(G M) / r^2

Question 60

In a radial field, you gain gravitational potential energy if you move away from...

Answer 60

The mass causing the field.

Question 61

Give the equation for gravitational potential energy in a radial field.

Answer 61

E grav = - (G M m) / r

Question 62

Where is potential energy defined as zero?

Answer 62

At an infinite distance away from the mass.

Question 63

Is gravitational potential energy at the Earth's surface positive or negative?

Answer 63

Negative.

Question 64

What is gravitational potential defined as?

Answer 64

The gravitational potential energy per unit mass.

Question 65

What are the units of gravitational potential?

Answer 65

J Kg^-1

Question 66

What is the symbol for gravitational potential?

Answer 66

V

Question 67

What is the equation for gravitational potential in a radial field?

Answer 67

V = -(G M) / r

Question 68

Where is gravitational potential defined as zero?

Answer 68

At an infinite distance away from the mass.

Question 69

What does the gradient of a E grav against radius graph represent?

Answer 69

The value of the gravitational force at that point.

Question 70

What does the gradient of a V against radius graph represent?

Answer 70

The gravitational field strength at that point.

Question 71

What is a satellite?

Answer 71

A small mass that orbits a far greater mass.

Question 72

How could you calculate the speed of an orbiting satellite?

Answer 72

Equate Newton's law of gravitation with F = (m v^2) / r and rearrange to make v the subject.