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Physics > unit 4 momentum > Flashcards

unit 4 momentum Flashcards

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1
Q

linear momentum

A

mass times velocity

vector quantity

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2
Q

resultant

A

rate of change of momentum

formula pg 1

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3
Q

force and change of momentum

newton’s second law states that

A

the rate of change of momentum is
proportional to the resultant force

and change of momentum takes place in the direction of the resultant force

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4
Q

force and change of momentum

derivation of F = ma Newton’s second law

A

pg 1

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5
Q

force and change of momentum

newton is defined as

A

the force to caused 1kg mass accelerates by 1 ms^-2

k = 1 
F = ma

pg 1

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6
Q

force and change of momentum

F = ma can only be used if

A

F in newton

m in kg and a in ms^-2

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7
Q

force and change of momentum

impulse , I

define and formula

A

is the change of momentum

I = change in mv = Ft

considers a single body
direction of impulse same as the direction of the resultant force acts on that body

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8
Q

force and change of momentum

impulse , I

graph F vs t

A

area under graph of force against time

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9
Q

momentum and kinetic energy

kinetic energy
2 formulas
original and derived

A

pg 2

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10
Q

momentum and kinetic energy

remember how the wind generator works?

A

pg 3

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11
Q

principle conservation of momentum

define

A

total momentum before collision same as
total momentum after collision
provided no external resultant force act on the system

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12
Q

derivation of conservation of momentum

from newton’s second and third law

A

pg 4

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13
Q

prove conservation of momentum by calculation

A

1.

  • calculate total momentum before collision
  • calculate total momentum after collision separately
  • compare the values and make valid conclusion
    • calculate change in momentum for A
    • calculate change in momentum for B
    • if the change of momentum of A = but opposite to change of B , momentum conserved
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14
Q

principle conservation of momentum

bouncing ball

A
  • momentum is conserved in the case of bouncing ball
  • the system is the ball and the earth
  • momentum of earth changes by the same amount
  • but in the opposite direction
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15
Q

principle conservation of momentum

explosion or radioactive decay

equation
explain conservation

A

equation pg 5

  • total momentum before is zero
  • total momentum after must be zero , principle conservation of momentum
  • less massive object with higher speed since equal magnitude of momentum
  • move in opposite direction
  • energy transferred from chemical or nuclear energy to kinetic energy. kinetic energy increases
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16
Q

principle conservation of momentum

if two particles are not ejected exactly in opposite directions , one is emitted at an angle

show KE proportional to mass

A

eq at pg 6

higher mass particles with smaller kinetic energy

17
Q

elastic collision

A

kinetic energy is conserved in the collision

18
Q

inelastic collision

A

kinetic energy before collision may be smaller or bigger than after collision

19
Q

elastic collision

kinetic energy
total energy
momentum

A

kinetic energy
total energy
momentum

all conserved

20
Q

inelastic collision

kinetic energy
total energy
momentum

A

kinetic energy - not conserved
total energy - conserved
momentum - conserved

21
Q

2 objects stick together

A

perfectly inelastic

22
Q

if separate after collision

A

either elastic or inelastic

23
Q

to prove collision is elastic by calculation

A
  • calculate total kinetic energies before collision
  • calculate total kinetic energies after collision separately
  • compare the values and make valid conclusion
24
Q

conservation of momentum in spring

initially the trolleys are not moving
then the thread is cut and the trolleys move apart

why the compression of spring is reduced, the momentum of trolley A is equal in magnitude but opposite in direction to the momentum of trolley B

A
  • momentum before release is zero
  • total momentum after release should also be zero since momentum is conserved , no external force acts on the trolley
  • so the momentum of trolley A is = magnitude but opposite in direction to the momentum of trolley B
25
Q

conservation of momentum in spring

initially the trolleys are not moving
then the thread is cut and the trolleys move apart

if mA > mB , which has higher kinetic energy at that instant when the compression of spring is zero

A
  • kinetic energy formula ..
  • equal magnitude of momentum ( formula proportional )
  • mA > mB
  • Ek B > EkA

Physics (12 decks)

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