9709 · 4.3
Momentum flashcards
Revision flashcards for Cambridge 9709 Momentum (syllabus 4.3). Flip, recall, then mark a real past-paper question.
Card
What is the definition of linear momentum?
Linear momentum is the product of an object's mass and its velocity. It is a vector quantity.
Card
What is the formula for momentum?
$p = mv$, where $p$ is momentum, $m$ is mass, and $v$ is velocity.
Card
What are the SI units for momentum?
Kilogram metres per second (kg m s⁻¹) or Newton seconds (N s).
Card
State the Principle of Conservation of Linear Momentum.
For a system of interacting objects, the total momentum remains constant, provided that no external resultant force acts on the system.
Card
What is a 'closed system' in the context of momentum?
A system on which no external forces are acting. For example, two particles colliding on a smooth horizontal plane where gravity and normal reaction cancel out.
Card
What is impulse?
Impulse is the change in momentum of an object. It is also equal to the product of the force acting on the object and the time interval for which it acts.
Card
What are the two key formulas for impulse?
$I = \Delta p = mv - mu$ (change in momentum) and $I = F \Delta t$ (force multiplied by time).
Card
What is the difference between an elastic and an inelastic collision?
In an elastic collision, both momentum and kinetic energy are conserved. In an inelastic collision, momentum is conserved but kinetic energy is not (it is usually converted to heat, sound, etc.).
Card
What happens when two particles coalesce?
They stick together and move with a common final velocity. This is a perfectly inelastic collision, where the maximum possible kinetic energy is lost.
Card
A common mistake is to forget that momentum is a vector. What does this mean for calculations?
You must define a positive direction. Any velocity in the opposite direction must be given a negative sign in your equations.
Card
How do you handle an explosion problem where an object starts from rest?
The initial momentum is zero. By conservation, the total momentum of all the fragments after the explosion must also be zero. The sum of the vector momenta of the fragments is zero.