This aesthetic, in-depth, neatly typed document summarises Section C of the IEB Grade 12 Physics syllabus:Momentum, Impulse, Work, Energy and Power . This document includes the full section C syllabus, all definitions, additional class notes, own research notes and all relevant diagrams.
Linear momentum: Product of the mass and velocity of an object.
Mass: Quantity of matter.
• Formula: p=m.v
¡1
• p: momentum : kg:m:s
• m: mass : kg
¡1
• v velocity: m:s
Impulse: Change in momentum: J or ¢p (not SAG de nition)
J = impulse = Fnet¢t
¡1
NOTE: kg:m:s = N :s
Law of conservation of linear momentum: Total linear momentum of an isolated system is constant
Isolated system: System that has no net external forces acting on it (friction and air resistance need
to be negligible)
When 2 objects collide (or one object explodes into 2:
Ptotal before = Ptotal after
(NOT ¢p )
Formula works as follows:
If 2 objects collide, then: ¢P A = ¡¢P B
(Ptot after - Ptot before)
Elastic collisions: Collision in which both linear momentum and kinetic energy are conserved
Inelastic collision: Collision in which momentum is conserved but kinetic energy in NOT.
fi
, When asked to determine if a collision is elastic or inelastic, Calculate Ektoti and Ektotf separately
and compare
1
Ektoti = Ek of the system: Ek = m:v 2
2
Impulse: Change in momentum: J or ¢p
¢p = m:¢V (mass is of one speci c object)
¢p = pf ¡ pi
= m:Vf ¡ m:Vi
Impulse: (SAG de nition): Product of the net force and contact time
(Vector quantity in same direction as net force vector)
J = Fnet:¢t
Impulse-momentum theory:
Fnet:¢t = m:¢V
• To calculate impulse on object A:
J = Fnet:¢t
= ¢p
= m:Vf ¡ m:Vi
Newton's Second Law in terms of momentum: The net force acting on an object is equal to the rate
of change of momentum.
Crumple zone:
¢p is the same (constant)
¢p
From: Fnet = • Fnet is inversely proportional to contact time
¢t
• When contact time is increased, net force is decreased
1 • Crumple zone extends contact time, therefore total force is decreased
Fnet®
¢t
fi
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