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True or False?
Momentum is a scalar quantity.
False.
Momentum is a vector quantity as it has both magnitude and direction.
Define momentum.
Momentum is the product of an object's mass and velocity.
True or False?
An object at rest has momentum.
False.
An object at rest has zero velocity, so zero momentum.
What is the equation of momentum?
The equation of momentum is
Where:
= momentum, measured in kilogram metres per second (kg m/s)
= mass, measured in kilograms (kg)
= velocity, measured in metres per second (m/s)
True or False?
Momentum can be either positive or negative.
True.
Momentum can be either positive or negative because it is a vector quantity.
What are the three conditions under which the momentum of an object will change?
The three conditions under which the momentum of an object will change are:
if the object's velocity changes
if the object's direction changes
if the object's mass changes
What is the principle of conservation of momentum?
The principle of conservation of momentum states that the total momentum before an interaction equals the total momentum after the interaction, if no external forces are acting on the objects.
True or False?
The conservation of momentum applies only to single objects.
False.
The conservation of momentum applies to systems of objects, which can include one or multiple objects.
State the condition for momentum to be conserved in a collision.
Momentum is conserved in a collision if there is no net external force acting on it, and energy within the system remains constant.
Define force in terms of momentum.
Force is the rate of change of momentum on an object.
State the equation for the change in momentum of an object.
The equation for the change in momentum of an object is
Where:
= change in momentum, measured in kilogram metres per second (kg m/s)
= mass, measured in kilograms (kg)
= final velocity, measured in metres per second (m/s)
= initial velocity, measured in metres per second (m/s)
True or False?
Force can be expressed as the change in velocity over time.
False.
Acceleration is expressed as the change in velocity over time. Force can be expressed as the change in momentum over time.
State the equation for force as the rate of change in momentum.
The equation for force as the rate of change in momentum is
Where:
= force, measured in newtons (N)
= mass, measured in kilograms (kg)
= final velocity, measured in metres per second (m/s)
= initial velocity, measured in metres per second (m/s)
= time, measured in seconds (s)
If an object has a positive momentum before a collision and a negative momentum after a collision, what does this imply about the motion of the object?
A positive momentum before a collision and a negative momentum after a collision implies that the object has changed direction.
True or False?
The shorter the time over which the momentum changes, the smaller the force experienced by the object.
False.
The shorter the time over which the momentum changes, the larger the force experienced by the object.
Define Newton's third law of motion.
Newton's third law of motion states that whenever two objects interact, the forces they exert on each other are equal in magnitude and opposite in direction.
What are the three rules for identifying third law pairs of forces?
The three rules for identifying third law force pairs are:
the forces act on different objects
the forces are equal in magnitude but opposite in direction
the forces are the same type
True or False?
A water bottle exerts a push force on a table, and the table exerts a push force on the water bottle. This is an example of Newton's third law.
True.
The water bottle exerts a push force (reaction force) on the surface of the table and the table exerts a push force (reaction force) on the water bottle that is equal in magnitude but opposite in direction. This is an example of Newton's third law.
True or False?
There is a weight force and a reaction force acting on a person that are equal in magnitude and opposite in direction. This is an example of Newton's third law.
False.
The weight force and the reaction force are both acting on the same object, the person, and the forces are different types (weight and reaction force). Therefore, this is not an example of Newton's third law.
True or False?
A ball collides with a wall, exerting a push force on the wall. The wall exerts a push force on the ball, and the ball bounces off the wall. This is an example of Newton's third law.
True.
The ball exerts a push force on the wall, and the wall exerts a push force on the ball that is equal in magnitude and opposite in direction. This is an example of Newton's third law.
True or False?
Particle A collides with particle B.
False.
If particle A collides with particle B, then the force exerted by A on B will be equal in magnitude but opposite in direction to the force exerted by B on A.
True or False?
The force of an impact in a vehicle collision can be decreased by increasing the contact time over which the force acts.
True.
The force of an impact in a vehicle collision can be decreased by increasing the contact time over which the force acts.
Name one example of a safety feature designed to reduce the impact of a force during a collision.
Examples of safety features designed to reduce the impact of a force during a collision are:
seatbelts
air bags
crumple zones
helmets
crashmats
playground floors
How does an air bag reduce the risk of injury to a passenger?
An air bag inflates upon impact. The air bag increases the contact time over which the passenger's momentum changes to zero, and therefore decreases the force experienced by the passenger. This reduces the risk of injury to the passenger.
True or False?
Safety features can prevent injuries in all cases of use.
False.
Safety features can reduce the risk of serious injury but cannot completely prevent it.