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Lecture8 (Topic7)
Momentum, Impulse and Collisions, NG HUI YUN
A20SC0187…
Lecture8 (Topic7)
Momentum, Impulse and Collisions
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Conservation of Momentum
LAW OF CONSERVATION OF MOMENTUM
The total momentum of an isolated system of objects remains constant.
m₁v₁+m₂v₂=m₁v₁'+m₂v₂'
There are 2 types of force,
internal force and external force.
In Newton's third law of motion,
internal forces cancel each other in pairs.
Impulses
F=dp/dt
dp=Fdt
Impulse, J=△p=Fdt
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Collisions
Elastic Collisions:
Conservation of Kinetic Energy
½m₁v₁²+½m₂v₂²=½m₁v₁'²+½m₂v₂'²
v₁-v₂=-(v₁'-v₂')
*valid only for head-on 1D elastic collisions
Inelastic Collisions
Even kinetic energy is not conserved,
total energy is conserved.
K₁+K₂=K₁'+K₂'+thermal and other form of energy
Complete Inelastic Collisions:
-2 objects stick tgt after collision
-MAX KE is transferred to other forms consistent with conservation of momentum
Centre of Mass (CM)
Even object rotates/several parts of system move relative to one another,
there is one point (CM) that moves in the same path that a particle would move if subjected to the same net force.
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Translational Motion of CM
CM of a system moves like a single particle of mass M acted upon by same net Fext.
System of Variable Mass
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