Topic 2 - Mechanics

Question 1

What is displacement?

Answer 1

The distance in a given direction from a fixed reference point

Question 2

What is velocity?

Answer 2

The rate of change of displacement with time (speed with a direction)

Question 3

What is speed?

Answer 3

The rate of change of distance with time

Question 4

What is acceleration?

Answer 4

The rate of change of velocity with time

Question 5

What is the difference between instantaneous and average values?

Answer 5

An instantaneous value gives a value at an exact instant.

An average value gives an average value for a fixed amount of time.

Question 6

What is the final velocity of an object when its acceleration is uniform?

Answer 6

v = u + at

Question 7

What is the acceleration of a body falling in a vacuum near the Earth’s surface?

Answer 7

g = 9.81 ms^–2

Question 8

What is the effect of air resistance on falling objects?

Answer 8

• Air is forced to move out of the path of the object
• As air resistance increases, the rate of increase in velocity becomes less
• Eventually the object reaches a constant, maximum speed known as the terminal velocity

A: no air resistance

B: yes air resistance

Question 9

What does an object’s terminal velocity depend on?

Answer 9

1. Cross-sectional area
2. Shape
3. Weight

Question 10

How can the velocity be found in displacement–time graph?

Answer 10

By calculating the gradient of the line

Question 11

How can the instantaneous velocity be found from an exponential displacement–time graph?

Answer 11

By calculating the gradient of the tangent to the line at that instant

Question 12

How can the acceleration be found in a velocity–time graph?

Answer 12

By calculating the gradient of the line

Question 13

What is the area under a velocity–time graph equal to?

Answer 13

The change of displacement

Question 14

What is the area under an acceleration–time graph equal to?

Answer 14

The change of velocity

Question 15

Summarise the graphs of motion

Answer 15

Question 16

What is relative velocity?

Answer 16

The difference between two velocities measured in the same frame of reference

Question 17

What is the simplest form of a force?

Answer 17

A push or a pull

Question 18

What are accelerations caused by?

Answer 18

Forces (push)

Question 19

What can forces do to the shape of an object?

Answer 19

Alter it and cause deformation

Question 20

What are different types of forces

Answer 20

1. Weight
2. Tension and compression
3. Reaction forces
4. Friction and air resistance
5. Upthrust
6. Non-contact forces

Question 21

What is the expression for weight?

Answer 21

W = mg

Question 22

What is the rule of reaction forces?

Answer 22

If two objects are in contact with each other, then each must exert an equal force on the other

Question 23

What is air resistance?

Answer 23

A force that opposes motion

Question 24

What is friction?

Answer 24

Opposing force when objects are in contact

Question 25

What is upthrust?

Answer 25

A force exerted vertically upwards on any object which is in a fluid

Question 26

What are non-contact forces?

Answer 26

1. Gravitational force 2. Magnetic force 3. Electric force 4. Nuclear forces

Question 27

What are the components of forces for the following diagram?

Answer 27

F_A = mgsinθ F_B = mgcosθ

Question 28

What is Newton's first law of motion?

Answer 28

An object will remain at rest, or continue to move in a straight line at a constant speed, unless a resultant force acts on it

Question 29

What is translational equilibrium?

Answer 29

An object that has no resultant force acting on it is saidto be in translational equilibrium (resultant force is zero)

Question 30

What are examples of Newton's first law?

Answer 30

1. Objects at rest with no sideways forces 2. Horizontal motion at constant velocity 3. Vertical motion of falling objects 4. Horizontal acceleration

Question 31

How can equilibrium be achieved for a mass that is not in equilibrium?

Answer 31

If two forces are acting on an object, a third external force can be added that is equal in magnitude to the resultant force of the other two

Question 32

What is Newton's second law of motion?

Answer 32

Acceleration is proportional to the force: F = ma Force equals the rate of change of momentum:

Question 33

What is linear momentum?

Answer 33

Mass multiplied by velocity p = mv

Question 34

What is impulse?

Answer 34

The product of force and the time for which the force acts impulse = F∆t = m∆v

Question 35

What is the area under a force–time graph equal to?

Answer 35

The impulse (change of momentum)

Question 36

What is said about the conservation of momentum?

Answer 36

All momentum is conserved. Always true with no exceptions

Question 37

What is Newton's third law of motion?

Answer 37

To every action there is an equal and opposite reaction

Question 38

What are examples of Newton's third law?

Answer 38

1. If you pull a rope, the rope pulls you 2. If the Earth pulls a person, the person pulls the Earth 3. If a fist hits a cheek, the cheek hits the fist 4. If the Sun attracts the Earth, the Earth attracts the Sun 5. If a boat pushes down on the water, the water pushes up on the boat

Question 39

What is work?

Answer 39

The energy transfer that occurs when an object is displaced by using a force

Question 40

What is the work done if the force is constant and in the same direction as movement?

Answer 40

W = Fs

Question 41

What is the work done if the force is not in the same direction as the displacement?

Answer 41

W = Fscosθ

Question 42

What is the area under a force–displacement graph?

Answer 42

Work done

Question 43

What are different forms of energy?

Answer 43

1. Gravitational (potential) energy 2. Nuclear (potential) energy 3. Chemical (potential) energy 4. Electric (potential) energy 5. Elastic strain (potential) energy 6. Thermal energy (heat) 7. Radiant energy 8. Kinetic energy 9. Internal energy 10. Mechanical wave energy (sound and water waves)

Question 44

What is potential energy?

Answer 44

Stored energy. Potential energies exist where there are forces between objects

Question 45

What is kinetic energy?

Answer 45

Energy that involves moving objects

Question 46

What are types of energies that transfer energy?

Answer 46

1. Electrical energy 2. Thermal energy 3. Radiant energy 4. Mechanical waves

Question 47

What is the principle of conservation of energy?

Answer 47

Energy cannot be created or destroyed, it can only be transferred from one form to another. (the total amount of energy in the universe is constant)

Question 48

What is the change in graviational potential energy?

Answer 48

∆E_P = mg∆h

Question 49

What is the formula for kinetic energy?

Answer 49

E_K = 1/2mv²

Question 50

What is the equation for kinetic energy with momentum?

Answer 50

Useful when dealing with the motion of atomic particles

Question 51

What are the equations for doing work to change motion?

Answer 51

Question 52

What is an elastic collision?

Answer 52

A collision in which the total kinetic energy of the masses is the same before and after.

Question 53

What is an inelastic collision?

Answer 53

A collision in which some or all kinetic energy is transferred to other forms of energy

Question 54

What is power?

Answer 54

The rate of transferring energy

Question 55

What is the power transferred when travelling at constant velocity?

Answer 55

P = Fv

Question 56

What is efficiency?

Answer 56

Question 57

Draw a vector diagram to illustrate that the acceleration of a particle moving with constant speed in a circle is directed towards the centre of the circle

Answer 57

- The velocities are always directed along tangents to the circle - A centripetal force is always acting perpendicularly to the velocity, inwards towards the centre - Resultant force acting on the mass has the same magnitude but continuously changing direction

Question 58

What is the expression for centripetal acceleration?

Answer 58

Question 59

What is the force needed to make a mass move in a circle at constant speed?

Answer 59