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Physics > Moments And Momentum > Flashcards

Moments And Momentum Flashcards

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1
Q

What is the definition of centre of mass

A

The centre of mass is defined as the point on an object where all the mass acts through.

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2
Q

Where is the centre of mass in a regular shaped object

A

The centre

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3
Q

Describe a practical to find the centre of mass of an irregular shaped piece of card

A

Hang a pendulum from the cork. Place the pin in a hole in the sheet, then put it into the cork. Allow the card to rest, without touching it, so it can be used to measure. Draw a line on the card to show the position of the string behind the card. Repeat this 3 times, then view the point at which the lines intersect. This is the centre of mass of the card.

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4
Q

Why does an object topple

A

The centre of mass/gravity acts outside the base of the object

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5
Q

What factors make an object less stable (2)

A
  1. A smaller base
  2. A higher centre of gravity
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6
Q

When does toppling happen relative to moments

A

When the clockwise and anticlockwise moments are not balanced

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7
Q

Centre of gravity vs centre of mass

A

Centre of gravity depends upon the gravitational field, but centre of mass does not.

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8
Q

What is the principle of momentum

A

The momentum before and after a collision gets conserved unless an external force acts on the system

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9
Q

What is the principles of momentum formula

A

Pbefore = Pafter

M1U1=M2U2=M1V1+M2V2

M - mass
U - initial velocity
V - final velocity

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10
Q

What are the three types of collisions and what do they mean

A

Elastic - momentum and kinetic energy are conserved
Inelastic - momentum is conserved, but kinetic energy is not conserved
Explosion - momentum is conserved, initial momentum is always zero. Kinetic energy is conserved.

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11
Q

What is the definition of momentum

A

A conceptual measure of how difficult it is to stop an object, taking into account mass and velocity to find out the energy required to stop it

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12
Q

What is the equation for momentum

A

Momentum = mass x velocity

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13
Q

What are the units for momentum

A

kg m/s (Kilograms metres per second)

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14
Q

Is momentum a vector or a scalar

A

Vector

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15
Q

When does momentum change

A

If a force acts on a body which is moving or is able to move

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16
Q

Is kinetic energy a vector or a scalar

A

Scalar

17
Q

What is:
1. Scalar x scalar
2. Scalar x vector
3. Vector x vector

A
  1. Scalar
  2. Vector
  3. Scalar
18
Q

What is the definition of the moment of a force

A

The size of the force multiplied by the perpendicular distance to the pivot

19
Q

What is the equation for moments

A

Moment = force x perpendicular distance to the pivot

20
Q

What are the units for moments

A

Nm (newtonmeters)

21
Q

What is the sum of the clockwise moments and the anticlockwise moments in equilibrium

A

They are equal

22
Q

What is the moment size if the force is on the pivot

A

0Nm

23
Q

What is the moment size if the force is on the pivot

A

0Nm

24
Q

Are moments scalar or vector

A

Vector

25
Q

What is the definition of impulse

A

A measure of the change of momentum

26
Q

Does impulse look at the whole system or just one object

A

One object only e.g. one car in a multi-car crash

27
Q

What are the units for impulse

A

KG m/s OR Ns (newtonseconds)

28
Q

What letter is used to represent impulse

A

ΔP (change in momentum)

29
Q

What is one equation used for impulse

A

ΔP = M(V-U)

M - mass
V - final velocity
U - initial velocity

30
Q

What equation links force, impulse and time

A

ΔP/ΔT = F

Note that ΔT is the same as just using T

31
Q

What are 3 safety features in a car

A
  1. Seatbelt
  2. Airbag
  3. Crumple zone
32
Q

How do car safety features protect humans in the event of a crash? Use an equation to aid your answer

A

They increase the time taken for the momentum of the person to reach zero, so decreases the force on them using the equation:

ΔP/ΔT = F

Physics (12 decks)

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