Topic 2 Flashcards
What must always be true when using the SUVAT equations of motion?
The acceleration must be unifrom - if the acceleration is changing, the equations are not valid.
What does the gradient of a distance-time graph represent?
Speed
What does the gradient of a displacement-time graph represent?
Velocity
What does the gradient of a velocity-time graph represent?
Acceleration
Describe the shape of a velocity-time graph for an object travelling with unifrom acceleration.
If accleration is constant, the gradient of the velocity-time graph will be constant and so it will form a straight line graph.
Describe the shape of a velocity-time graph for an object travelling with non-uniform acceleration
If acceleration is not constant, the gradient of the velocity-time graph will change and so it will form a curve
Compare the velocity-time graphs for a uniformly accelerating and a uniformly decelerating object.
For an accelerating object, the gradient will be positive
For a decelerating object, the gradient will be negative
What is a scalar quantity
A scalar quantity is one that has a magnitude but not a fixed direction
What is a vector quantity
A vector quantity is one that has a magnitude and a fixed direction
Give five eamples of scalar quantities
Distance, Speed, Mass, Energy, Temperature
Give five examples of vector quantities
Displacement, Velocity, Acceleration, Momentum, Force
How is a vector quantity represented on a diagram?
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
What does resolving a vector involve?
Splitting the vector into two perpendicular components, vertical and horizontal.
Define the horizontal component of the vector in terms of V and θ
x = Vcos(θ)
Define the verticle component of the vector in terms of V and θ
y = Vsin(θ)
Describe the relationship between the perpendicular components of a vector
The perpendicular components are independent of each other
How should the components of a projectile be handled when carrying out calculations
The horizontal and vertical components are independent of each other and so should be treated separately
SUVAT should be used separately for each component
If a projectile is moving freely under gravity, what can be said about the vertical acceleration?
The vertical accelaration will be the acceleration due to gravity and so will have a magnitude of 9.81m/s^2
State Newton’s first law of motion in words
An object at rest will remain at rest, and an object moving with a given velocity will continue moving with that same velocity, unless acted on by an external resultant force.
State Newton’s second law of motion in words
The acceleration of an object is directly proportional to the resultant force acting on it and inversely proportional to its mass.
State the defining equation of Newton’s second law of motion.
F=ma
Force (N) = Mass (kg) x Acceleration (m/s^2)
Can an object travelling with constant speed change direction, without an external force acting?
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.
Describe the forces acting on an object travelling at terminal velocity
The forces are balanced in both the vertical and horizontal components of its motion
There is no resultant force, and therefore no acceleration
What is meant by terminal velocity?
For a given set of conditions, the terminal velocity is the maximum speed of the object. An object has zero acceleration at terminal velocity
State the equation used to calculate the weight of an object
W=mg
Weight = Mass x Gravitational Field Strength
What is the unit of weight?
Newtons, N
State Newton’s third law of motion in words.
Every action has an equal and opposite reaction. This means that there is always a pair of forces acting on interacting objects, equal in magnitude, but in opposite directions
State the equation for momentum
p=mv
Momentum = Mass x Velocity
What is the unit of momentum?
kgm/s
What is the consequence of the linear conservation of momentum
The total momentum of a system before an event is always equal to the total momentum of the system after the event.
What is a moment?
A moment is the turning effect of a force
State the equation used to calculate the moment of a force.
Moment of a force = Force x Distance
What distance must be used when calculating a moment?
The perpendicular distance between the line of action of the force and the axis of rotation
What is the unit of a moment?
Nm
What is the principle of moments?
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
What is an object’s centre of gravity
The single point through which the object’s entire weight can be said to act
What will occur if the line of action, an object’s centre of gravity, lies outside its base?
The object’s weight will produce a resultant moment and so if unsupported, the object may topple.
State the equation used to calculate the work done by a force
W=FΔs
Work Done = Force x Change in Distance
What force is used when calculating the work done by a force over a distance?
The component of the force that is in the direction of the object’s motion
What is the unit of work?
Joules, J
What is the work done by the force, F when it moves the object a distance of x? (Triangle with angle θ, hypotinuse of F, horizontal x)
Work Done = Fcos(θ) x
What form of energy do all moving objects have?
All moving objects have kinetic energy
State the equation used to calculate the kinetic energy of an object
Ek = 1/2 mv^2
Kinetic energy = 1/2 x Mass x Velocity^2
What form of energy does a raised object have?
Gravitational Potential energy
State the Equation used to calculate gravitational potential energy
GPE = Mass x Gravitational Field Strength x Height GPE = mgh
What is the conservation of energy?
The law of conservation of energy states that energy cannot be created or destroyed - it can only be transferred between different forms
What is power
The rate at which energy or work is done
State two equations used to calculate power
P=E/t
P=W/t
What is the unit of power?
Watt, W
What is the waste energy of an electrical appliance?
The waste energy is the energy that is not used for the appliance’s intended purpose.
State the equation relating energy and efficiency
Efficiency = Useful energy output / Total energy input
State the equation relating power and efficiency
Efficiency = Useful power output / Total power input
What is the unit of efficiency?
Efficiency is a ratio and so doesn’t have an associated unit
