Grade 12 IEB Physical Science (Physics) Momentum, Impulse, Work, Energy and Power (Section C) Summary & notes

Momentum, Impulse, Work, Energy and Power:


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.




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, 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




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