Mechanics Flashcards
What must always be true when using the SUVAT equations of motion?
The acceleration must be uniform- 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 uniform acceleration
If acceleration is constant, the gradient of the velocity-time graph will be constant and so it will from 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 examples 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
Define the horizontal component of a vector at an angle to the horizontal in terms of V and theta.
horizontal component: X = V cos theta
Define the vertical component of a vector at an angle to the horizontal in terms of V and theta.
Vertical component: y = V sin Theta
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? (2)
- 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 acceleration will be the acceleration due to gravity and so will have a magnitude of 9.81 ms {-1}
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.
Resultant Force (N) = Mass(kg) x Acceleration (ms{-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.
Weight = Mass x Gravitational Field Strength
What is the unit of weight?
Newton, 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 of momentum.
p = mv
What is the unit of momentum?
Kgms{-1}
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.
State the equation used to calculate the work done by a force.
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 a force F at an angle to the horizontal when direction of motion is on the x-axis?
work done= F cos theta x distance travelled
what form of energy do all moving objects have?
All moving objects have kinetic energy.
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
What is the conservation of energy?
The law of conservation of energy states that energy cannot be created of 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 appliance’s intended purpose.
State the equation relating energy and efficiency.
Efficiency = [Useful Energy Output] / [ Total Energy Input]
What is the unit of efficiency?
Efficiency is a ratio and so doesn’t have an associated unit.
In an elevator what is the resultant force equals to?
Weight of the elevator - the tension on the cable holding the elevator
A ball is hanging on a string. Explain why the tension in the string increases immediately after the ball is kicked.
- The ball accelerates towards centre of the circular path created by the string
- This results in a force acting upwards on the string
- this adds to the tension and thus the increase
For a vertical string, what is the tension of the string?
T = mg + ma
