Describing motion along a line (5.6.1) (M) Flashcards
What is distance?
how far an object moves
What type of quantity is distance?
scalar - does not involve direction
What is displacement?
A measure that includes both the distance an object moves, measured in a straight line from the start point to the finish point and the direction of that straight line
What type of quantity is displacement?
vector
What type of quantity is speed?
scalar - does not involve direction
The speed of a moving object is (…) constant. When people walk, run or travel in a car their speed is (…)
rarely
constantly changing
4 needed
What are some factors that can affect the speed at which a person can walk, run or cycle
- age
- terrain
- fitness
- distance travelled
What is the typical speed of walking?
∼ 1.5 m/s
What is the typical speed of running?
∼ 3.0m/s
What is the typical speed of cycling?
∼ 6.0m/s
What are the typical speeds of a car, train and aeroplane?
car - 13/30m/s
train - 50m/s
aeroplane - 250m/s
Do the speed of sound and the speed of the wind vary or stay the same?
vary
What is the typical value for the speed of sound in air?
330m/s
What is the velocity of an object?
its speed in a given direction
What type of quantity is velocity?
vector
How can something in a circular motion (e.g. satellites), have constant speed but have changing velocity?
If something is in circular motion, its direction is constantly changing
How can the speed of an object e calculated from a distance-time graph?
Calculate the gradient
How can speed at any particular time be determined from a distance-time graph?
by drawing a tangent at that point and measuring the gradient
What is acceleration?
the rate of change of velocity
How would you describe an object that is slowing down?
It is decelerating
Falling objects accelerate at (…)m /s2
10
A typical acceleration for a car is (…)m/s2
5
How can the acceleration be calculate from a velocity-time graph?
Calculating the gradient
How can the distance travelled by an object (or displacement of an object) can be calculated from a velocity-time graph?
by calculating the area under the graph
may need to find area using triangles or trapezium area calculations
What is uniform acceleration?
When the rate of change of velocity is constant
v2 - u2 = 2as
Explain what happens when an object falls through a fluid
An object falling through a fluid initially accelerates due to the force of gravity.
Eventually the resultant force will be zero and the object will move at its terminal velocity (no resultant force, velocity constant so acceleration is zero)
4 marker
Why does a car have a maximum speed?
there is a maximum forward force (provided by the motor)
as the speed of the car increases, air resistance increases
until air resistance is equal in size to forward force
so the car can no longer accelerate
4 marker (indicative)
Describe what happens to the braking distance if speed doubles (refer to kinetic energy in the answer)
- doubling speed increase the kinetic energy
- kinetic energy increases by a factor of 4
- work done (by brakes) to stop the car increases
- work done increases by a factor of 4
- work done is force × distance and braking force is constant
- so if work done increases by 4 then the braking distance must increase by 4
How would changing the shape of a car so that it is more streamlined affect its top speed?
decreases surface area
so less air resistance
so reaches a higher speed
In circular motion, in which direction is the resultant force?
Towards the centre
2 marks - key exam technique
As an object moves along a runway, its acceleration decreases even though the force/power remains constant, why is this?
As speed increases, air resistance increases
reducing the resultant force
4 marks
Explain the changing motion of the skydiver in terms of the forces acting on the skydiver
initially air resistance is less than weight / gravity so the skydiver accelerates
acceleration causes the air resistance to increase
resultant force decreases to zero
so the skydiver falls at terminal velocity
3 marks
Explain why a skydiver reaches a much higher speed when jumping from a higher height?
The higher the altitude the less dense the air
so air resistance on the skydiver was less
so skydiver was able to accelerate for a longer time before reaching terminal velocity