P5 - Forces and motion Flashcards
Does a distance quantity require a
specific direction? i.e. Is it a scalar or
vector quantity?
No specific direction is required so it is a
scalar quantity.
If an object moves 3 metres to the left
and then 3 metres back to its initial
position, what is the object’s total
displacement?
● The object has zero displacement
● Displacement is a vector quantity so it also
involves direction
● The object starts and ends at the same point
State a typical value for the speed of
sound.
330 m/s
What is a typical value for human
walking speed?
1.5 m/s
What is a typical value for human
running speed?
3 m/s
What is a typical value for human cycling
speed?
6 m/s
State the equation linking distance,
speed and time. Give appropriate units.
Distance = Speed x Time
Distance (m), Speed (m/s), Time (s)
Why can an object travelling at a constant speed in a circle not have a constant velocity?
(Higher)
● Speed is a scalar quantity
● Velocity is a vector quantity which means it can
only be constant if the direction is constant
● In circular motion, the direction is continuously
changing
How can speed be calculated from a
distance-time graph?
The speed is equal to the gradient of the
graph.
What must be done to calculate speed at
a given time from a distance-time graph
for an accelerating object? (Higher)
● Drawing a tangent to the curve at the required time
● Calculating the gradient of the tangent
State the equation for the average acceleration of an object. Give appropriate units.
change in velocity (m/s) / time (s) = acceleration (m/s2)
How can the distance travelled by an
object be calculated from a velocity-time
graph? (Higher
It is equal to the area under the graph
Give an approximate value for the
acceleration of an object in free fall
under gravity near the Earth’s surface.
9.8 m/s²
What can be said about the resultant force acting on an object when it is falling
at terminal velocity?
● The resultant force is zero
● When at terminal velocity, the object is moving at a constant speed and so isn’t accelerating
State Newton’s first law for a stationary
object.
If the resultant force on a stationary
object is zero, the object will remain at
rest.
State Newton’s first law for a moving
object.
If the resultant force on a moving object
is zero, the object will remain at constant
velocity (same speed in same direction).
What can be said about the braking
forces and driving forces when a car is
travelling at constant velocity?
The braking forces are equal to the
driving forces.
If an object changes direction but
remains at a constant speed, is there a
resultant force?
Since there is a change in direction,
there is a change in velocity and so there
must be a resultant force.
What is inertia? (Higher)
The tendency of an object to continue in
its state of rest or uniform motion.
State the defining equation for Newton’s
Second Law.
Resultant force = Mass x Acceleration
F = ma
State Newton’s Second Law in words.
An object’s acceleration is directly
proportional to the resultant force acting
on it and inversely proportional to its
mass.
What is inertial mass? (Higher)
● A measure of how difficult it is to
change a given object’s velocity
● The ratio of force over acceleration
What is the symbol used to represent an
approximate value?
What is the symbol used to represent an
approximate value?
State Newton’s Third Law.
Whenever two objects interact, the
forces that they exert on each other are
always equal and opposite.
What is the stopping distance of a
vehicle equal to?
The sum of thinking distance and braking
distance.
For a given braking distance, if the
vehicle’s speed is increased, what can
be said about its stopping distance?
The stopping distance is increased with
an increase in speed.
Give a typical range of values for human
reaction time.
0.2 seconds - 0.9 seconds
Give three factors which can affect a
driver’s reaction time.
- Tiredness
- Drugs
- Alcohol
Give two factors which may affect
braking distance.
- Adverse (wet/icy) road conditions
2. Poor tyre/brake conditions
Describe the energy transfers that take
place when a car applies its brakes.
● Work is done by the friction force between
the brakes and wheel
● Kinetic energy of the wheel is converted to
heat and is dissipated to the surroundings
through the brake discs
To stop a car in a given distance, if its
velocity is increased, what must happen
to the braking force applied?
The braking force must also be
increased.
State two consequences of a vehicle
undergoing very large decelerations.
- Kinetic energy converted to heat is
very high causing brakes to overheat - Loss of control of the vehicle
