Linear Momentum & its Conservation (Cambridge (CIE) A Level Physics): Flashcards
Exam code: 9702
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Define the principle of conservation of momentum.
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Cards in this collection (15)
Define the principle of conservation of momentum.
The total linear momentum before a collision is equal to the total linear momentum after a collision, unless the system is acted on by a resultant external force.
Why can two objects moving in opposite directions have a total momentum of zero?
Momentum is a vector quantity, so opposing momenta (in opposite directions) can cancel out to give a net momentum of zero.
Define a closed (or isolated) system, in the context of momentum.
A system with no external forces acting on it.
Distinguish between internal and external forces acting on a system.
Internal forces are exchanged between particles within the system, e.g. tension in a string
External forces act on the system from outside, e.g. friction and weight
An object rebounds after colliding with another object. How does its velocity after the collision compare with its velocity before?
Its velocity reverses direction — for example, a positive velocity before the collision becomes negative after (or vice versa).
How can you determine whether a collision is elastic or inelastic?
Compare the total kinetic energy of the system before and after the collision — if kinetic energy is conserved, the collision is elastic; if it is not conserved, the collision is inelastic.
True or False?
In an inelastic collision where two objects stick together, momentum is not conserved.
False.
Momentum is always conserved, even in an inelastic collision — it is kinetic energy that is not conserved.
In two dimensions, momentum (a vector) can be resolved into its .......... and .......... components.
In two dimensions, momentum (a vector) can be resolved into its x and y components.
Define an elastic collision.
A collision in which all of the kinetic energy of the system is conserved.
Define an inelastic collision.
A collision in which kinetic energy is not conserved; some or all of the kinetic energy is transferred to other energy stores.
In a perfectly elastic head-on collision, how does the relative speed of approach compare with the relative speed of separation?
They are equal — the relative speed of approach equals the relative speed of separation.
What defines a "perfectly inelastic" collision?
A collision in which the two objects stick together and move as one body after the collision.
True or False?
Kinetic energy is always conserved in a collision, but momentum is not.
False.
Momentum is always conserved in a collision; kinetic energy is only conserved in an elastic collision.
Why does kinetic energy never have a negative value, even though velocity is a vector quantity?
Kinetic energy is a scalar quantity; since mass is scalar and v2 is always positive regardless of the direction of v, Ek is always positive.
In an inelastic collision, kinetic energy is transferred to other .......... stores.
In an inelastic collision, kinetic energy is transferred to other energy stores.
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