02 - Mechanics

Question 1

What must always be true when using the SUVAT equations of motion?

Answer 1

The acceleration must be uniform - if the acceleration is changing, the equations are not valid.

Question 2

What does the gradient of a distance-time graph represent?

Answer 2

Speed

Question 3

What does the gradient of a displacement-time graph represent?

Answer 3

Velocity

Question 4

What does the gradient of a velocity-time graph represent?

Answer 4

Acceleration

Question 5

Describe the shape of a velocity-time graph for an object travelling with uniform acceleration.

Answer 5

If acceleration is constant, the gradient of the velocity-time graph will be constant and so it will form a straight line graph.

Question 6

Describe the shape of a velocity-time graph for an object travelling with non-uniform acceleration.

Answer 6

If acceleration is not constant, the gradient of the velocity-time graph will change and so it will form a curve.

Question 7

Compare the velocity-time graphs for a uniformly accelerating and a uniformly decelerating object.

Answer 7

• For an accelerating object, the gradient will be positive
• For a decelerating object, the gradient will be negative

Question 8

What is a scalar quantity

Answer 8

A scalar quantity is one that has a magnitude but not a fixed direction.

Question 9

What is a vector quantity?

Answer 9

A vector quantity is one that has a magnitude and a fixed direction.

Question 10

Give five examples of scalar quantities.

Answer 10

1. Distance
2. Speed
3. Mass
4. Energy
5. Temperature

Question 11

Give five examples of vector quantities.

Answer 11

1. Displacement
2. Velocity
3. Acceleration
4. Momentum
5. Force

Question 12

How is a vector quantity represented on a diagram?

Answer 12

• As an arrow
• The direction of the arrow represents the direction of the quantity
• The length of the arrow represents the magnitude of the quantity

Question 13

What does resolving a vector involve?

Answer 13

Splitting the vector into two perpendicular components (vertical and horizontal

Question 14

How should the components of a proiectile be handled when carrying out calculations?

Answer 14

• The horizontal and vertical components are independent of each other and so should be treated separately
• SUVAT should be used separately for each component

Question 15

If a projectile is moving freely under gravity, what can be said about the vertical acceleration?

Answer 15

The vertical acceleration will be the acceleration due to gravity and so will have a magnitude of 9.81 ms.

Question 16

On a displacement/time graph what does a curve in the graph represent

Answer 16

Acceleration/deceleration

Question 17

What does the area under the graph of a velocity/ time graph represent

Answer 17

Displacement

Question 18

Which suvat equation would you use if u had : v , t , u and a

Answer 18

V = u + at

Question 19

Which suvat equation would you use if u had : a , t , u and s

Answer 19

S = ut + 1/2at^2

Question 20

Which suvat equation would you use if u had : u, v, a and s

Answer 20

v^2 = u^2 + 2as

Question 21

Which suvat equation would you use if u had : s, u, v, t

Answer 21

S = 1/2(u + v) t

Question 22

What does u stand for in the suvat equations

Answer 22

Initial velocity

Question 23

What does the v stand for in the suvat equations

Answer 23

Final velocity

Question 24

What are the 4 suvat equations

Answer 24

v = u+at
S = ut + 1/2at^2
v^2 = u^2 + 2as
S = 1/2 (u+v)t

Question 25

State Newton’s first law

Answer 25

An object will continue to move with uniform velocity, unless it is acted on by resultant external force

Question 26

What is newton’s second law?

Answer 26

F = ma Only uses when the object experiences a resultant force (is accelerating or decelerating)

Question 27

Can an object travelling with constant speed change direction, without an external force acting?

Answer 27

For an object to change direction, its velocity must change. This means there must be an acceleration. An acceleration cannot occur without an external resultant force acting.

Question 28

Describe the forces acting on an object travelling at terminal velocity.

Answer 28

• The forces are balanced in both the vertical and horizontal components of its motion • There is no resultant force, and therefore no acceleration

Question 29

What is meant by terminal velocity?

Answer 29

For a given set of conditions, the terminal velocity is the maximum speed of the object. An object has zero acceleration at terminal velocity.

Question 30

State the equation used to calculate the weight of an object.

Answer 30

W = mg Weight = Mass x Gravitational Field Strength

Question 31

State Newton’s third law

Answer 31

Every action has an equal and opposite reaction

Question 32

Describe in Newton’s third law pair of someone holding a mass

Answer 32

There is a normal contact force of it on you, and you are exerting a normal contact force on it

Question 33

What are the conditions for Newton’s third law?

Answer 33

Equal in magnitude Acting in opposite directions The same type of force Acting on different objects

Question 34

When talking about Newton’s third law, what would you describe weight as

Answer 34

Weight is a gravitational force

Question 35

What is the Newton’s third law pair of someone standing on Earth?

Answer 35

The gravitational force of the person on the Earth, and the gravitational force of the Earth on the person

Question 36

State the equation for momentum.

Answer 36

p = mv Momentum = Mass x Velocity

Question 37

What is the unit of momentum?

Answer 37

kgms^-1

Question 38

What is the consequence of the linear conservation of momentum?

Answer 38

The total momentum of a system before an event is always equal to the total momentum of the system after the event.

Question 39

What is the law of the conservation of energy?

Answer 39

Energy cannot be created or destroyed, only transferred from one energy store to another

Question 40

State the equation used to calculate the work done by a force.

Answer 40

W = F x s Work Done = Force × Change in Distance

Question 41

What force is used when calculating the work done by a force over a distance?

Answer 41

The component of the force that is in the direction of the object's motion.

Question 42

What is the unit of work?

Answer 42

Joules, J

Question 43

What is the work done by the force, F when it moves the object a distance of x? When F is at an angle

Answer 43

You work out the horizontal component so: Work Done = Fcos(angle)x

Question 44

What form of energy do all moving objects have?

Answer 44

All moving objects have kinetic energy.

Question 45

State the equation used to calculate the kinetic energy of an object.

Answer 45

Kinetic Energy = ½ × Mass × Velocity^2 E = ½ mv^2

Question 46

What form of energy does a raised object have?

Answer 46

Gravitational Potential Energy

Question 47

State the equation used to calculate gravitational potential energy.

Answer 47

GPE = Mass × Gravitational Field Strength x Height E = mgh

Question 48

What is power?

Answer 48

The rate at which energy or work is done.

Question 49

State 3 equations used to calculate power.

Answer 49

P= E/ t P = Work done / time P = force x velocity

Question 50

What is the unit of power?

Answer 50

Watt, W

Question 51

State the equation relating energy and efficiency.

Answer 51

Efficiency = Useful Energy Output / Total Energy Input

Question 52

State the equation relating power and efficiency.

Answer 52

Efficiency = Useful Power Output / Total Power Input

Question 53

What is the unit of efficiency?

Answer 53

Efficiency is a ratio and so doesn't have an associated unit.

Question 54

What is a moment?

Answer 54

A moment is the turning effect of a force.

Question 55

State the equation used to calculate the moment of a force.

Answer 55

Moment of a Force = Force × Distance

Question 56

What distance must be used when calculating a moment?

Answer 56

The perpendicular distance between the line of action of the force and the axis of rotation.

Question 57

What is the unit of a moment?

Answer 57

Nm

Question 58

What is the principle of moments?

Answer 58

For an object to be in equilibrium, the sum of the clockwise moments about a point must be equal to the sum of the anticlockwise moments.

Question 59

What is an object's centre of gravity?

Answer 59

The single point through which the object's entire weight can be said to act.

Question 60

How would you carry out an experiment working out the centre of gravity of an object

Answer 60

Punch 3 holes in each corner of the object. Attach a hanging mass to a needle and put it in a bung which is being held by a clamp stand. Draw a line from which the string/hanging mass goes over. Repeat for each hole. The point where all the lines cross is the centre of gravity

Question 61

What will occur if the line of action an object's centre of gravity lies outside its base?

Answer 61

The object's weight will produce a resultant moment and so if is unsupported, the object may topple.

Question 62

What is an elastic and an inelastic collision

Answer 62

Elastic- all kinetic energy and momentum is conserved Inelastic - some energy and momentum is lost