P10: Forces & Motion Flashcards
Does a distance require a specific direction?
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 objecy’s total displacement?
The object has zaero 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 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 s typical value for human cycling speed?
6 m/s
State the equation linking distance, speed and time?
Distance = Speed x Time
What must be done to calculate speed at a given time from a distance-time graph for an accelerating object?
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?
Acceleration = Change in velocity/time taken
How can the distance travelled by an object be calculated from a velocity-time graph?
It is equal to the area under the graph
What can be siad 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
What can be said about the braking forces and driving forces when a car is travellin* 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?
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?
A measure of how difficult it is to change a given object’s velocity
The ratio of force over acceleration
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 in increased wit( an increased in speed
Give a typical range of values for human reaction time?
0.2s - 0.9s
Give 3 factors which can affect a driver’s reaction time?
Tiredness
Drugs
Alcohol
Give 2 factors which may affect braking distance?
Adverse road conditions
Poor tyre conditions
State the equation used ro calculate momentum?
Momentum = mass x velocity
What is the unit for momentum?
Kg m/s
In a closed system, what can be said about the momentum before and after a collision?
The total momentum before is equal to the toatl momentum afterwards
State an equation linking change in momentum, force and time?
Force x Time = Change in momentum
What quantity is equal to the force experienced in a collision?
The rate of change of momentum
If an objectks momentum is foxed, what is the only way to reduce the force that the object experiences?
Increases the length of time over which the change of momentum occurs
