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GAMSAT March 2016 COPY > PHY 5 - Work > Flashcards

PHY 5 - Work Flashcards

1
Q

If displacement is zero, what is the work done ?

A

0.

Work done = Force x distance moved in direction of force

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2
Q

Why would you include Cos Ø to the work equation ?

A

To take into account that the force applied is not always at the same angle to the displacement. By using Cos Ø you seperate the force into vetical and horizontal components using the adjacent side.

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3
Q

What are the units of work ?

A

1 Joule (J) = 1 newton over 1 metre

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4
Q

Describe energy in terms of physics ?

A

Energy is a scaler, it is a physical quantity capable of producing work.

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5
Q

Name 8 different types of Energy

A
  • Mechanical
  • Electrical
  • Chemical
  • Potential
  • Kinetic
  • Sound
  • Atomic
  • Nuclear
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6
Q

What happens to the work done if the displacement is at 90º to the force ?

A

0 Work done because Cos 90 = 0.

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7
Q

What is the work done by the force normal ?

A

It is a counter-active force, therefore no work is done.

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8
Q

Describe the work done by friction ?

A

Always acts opposite to the direction of motion, Cos 180 º always = a negative value.

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9
Q

What equation summarises kinetic energy ?

A
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10
Q

What equation is described by the work-energy theorem ?

A

Change in kinetic energy + change in potential energy = Work

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11
Q

What is the equation for potential energy derived from the gravitation forces ?

A

Potential Energy = mgh

m = mass

g = gravity

h = height

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12
Q

Explain mechanical energy in relation to frictional forces ?

A

They are non-conservative forms of mechanical energy

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13
Q

What causes friction ?

A

Molecular adhesion between tangential surfaces- it is independent of the area of the surfaces touching each other.

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14
Q

What direction do frictional forces work on ?

A

They always oppose the motion

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15
Q

Name the two types of friction

A
  • Static
  • Kinetic
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16
Q

What is static friction ?

A

When the object is not moving, static friction is the force that must be overcome in order to move it.

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17
Q

Describe friction ?

A

A contact force that acts to oppose sliding motion between surfaces.

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18
Q

Explain when friction would be high or low ?

A

Increased if surfaces are dry and rough

Decreased if surfaces are wet and smooth

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19
Q

What is the Force Normal ?

A

The force perpendicular to the surface, typically equal and opposite to the gravitational force.

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20
Q

What is the coefficicent of friction ?

A

It is defined by the materials from which the two surfaces are made, and the relative roughess of the surfaces in contact.

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21
Q

What factors effect the amount of friction experienced by an object ?

A
  • The force normal
  • The coefficient of friction (µ)
22
Q

Sketch a diagram to demonstrate static friction

A
23
Q

What is kinetic friction ?

A

The force of friction when two surfaces are already moving relative to each other.

It is also the force that slows down a moving object when the force of static friction has been overcome.

24
Q

What is a normal value for a friction coefficient ?

A

Usually < 1

µ Kinetic is usually

25
Q

What are the units for the coefficient of friction ?

A

There are no units, it is just a numerical value.

26
Q

Sketch a graph of frictional force vs. Applied force

A
27
Q

How would you calculate Fmax ?

A
28
Q

What happens if F > µN ?

A

The object must accelerate because the maximal static frictional force has been overcome.

29
Q

Describe uniform circular motion

A

A particle moving in a circle at a constant speed.

30
Q

Why does uniform circular motion occur ?

A

Acceleration is due to a change in velocity. For a particle moving in a circle at a constant speed (uniform circular motion), the velocity vector changes continuously in direction, but the magnitude remains the same.

31
Q

What is centrepetal acceleration ?

A

The velocity is always tangent to the circle, the direction is always changing but the magitude remains the same. This creates an acceleration directed radically inward (ac) (Centre-seeking).

32
Q

How would you calculate the magnitude of ac ?

A

V2/R

Where r = radius of the circle

33
Q

What causes velocity ?

A

Velocity is the result of a net force acting on an object.

34
Q

How would you calculate the circumference of a circle ?

A

2πr

35
Q

How would you calculate the radius of a circle ?

A
36
Q

If a particle is moving in a circle, with non-uniform speed, what forces and accelerations will it experience ?

A
  • Cetripetal
  • Tangential
37
Q

What is the difference between the Centrifugal force and the Centripedal force ?

A
38
Q

What is Newton’s Second law ?

A
39
Q

What is the SI unit for friction ?

A

Kg/m/s2

40
Q

Compared to the force needed to start sliding an object across a rough, flat floor, the force required to keep the object in motion is… ?

A

Less !

Due to inertia, it is more difficult to get an object moving (overcome static friction) than it is to keep it moving.

41
Q

Describe mg in terms of physics forces

A

Mg = Mass x Gravity.

It is the force (weight) exerted by the object on the earth - this is the normal force that acts against gravity.

42
Q

What is potential energy ?

A

Energy accumulated by a system that contains it

43
Q

Define conservation of energy in terms of physics ?

A

The mechanical energy of a system (Er) = the sum of its Kinetic energy and it’s potential energy.

Er = Ek + Ep

44
Q

Describe the theorem of mechanical energy

A

The variation of the mechanical energy of a system is equal to the work of exterior forces acting on the system.

45
Q

What are the 3 components of the definition of mechanical force ?

A
  1. After a round trip, the Ke of a particle on which a force acts, must return to its initial value
  2. After a round trip, the work done on a particle by a force must equal zero
  3. The work done by the force on a particle depends on the initial and final positions of the particle and not on the path taken.
46
Q

Give an example of a non-conservative force ?

A

Friction

47
Q

Give an example of a conservative force ?

A

Gravity

48
Q

What is the SI unit for power ?

A

Watt (W) = 1 joule per second

49
Q

What equation describes power ?

A
50
Q
A

GAMSAT March 2016 COPY (26 decks)

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