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Mechanics > Work and Energy > Flashcards

Work and Energy Flashcards

1
Q

What is “Work done”?

A

When a force moves an object and energy is transferred.

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2
Q

How do you calculate Work done?

A

Work done = Force x distance, Work = Fd

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3
Q

What energy is transferred if a force of 2N moves a distance of 10m?

A

Work = Fd Work = 2N x 10m = 20J

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4
Q

If Work lifts an object against gravity what energy is gained?

A

Potential Gravitational Energy

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5
Q

Calculate the change in E^P (gravitational potential energy) when a person lifts 5kgs from the floor to a shelve 2m high.

A

E^p = mgh Ep = 5 x 10 x 2 = 100J

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6
Q

What is Kinetic Energy?

A

The energy of a moving object E^K

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7
Q

If an object is lifted higher what energy increases?

A

Gravitational Potential Energy (E^P)

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8
Q

How does energy move through a system?

A

Energy is transferred from object to object

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9
Q

What is happening to energy as an object falls?

A

E^P, Potential Gravitational Energy is transferred to E^K, Kinetic Energy

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10
Q

What energy is formed when the Kinetic energy of a moving car has the brakes applied?

A

E^K to Heat in the brakes and tires

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11
Q

What energies are formed when the Kinetic energy of a Wind turbine is transferred?

A

Electrical, heat and sound.

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12
Q

What energy is formed when a Roller coaster wagon is pulled up a ramp?

A

Gravitational Potential, heat and sound

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13
Q

The amount of kinetic energy of an object relates to which to factors?

A

Mass (m) and speed (v)

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14
Q

What is the calculation for E^K, Kinetic Energy?

A

E^K = ½mv^2

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15
Q

What happens to E^K if the speed is doubled?

A

4 x E^K

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16
Q

What happens to EK if the speed is trebled?

A

9 x E^K

17
Q

Calculate the Kinetic energy of a car with a mass of 800kg traveling at a speed of 10ms^-1

A

E^K = ½mv^2 E^k = ½800 x 102

E^K = 400 x 100 = 40000 J

18
Q

How much Work is needed to stop a 800kg car traveling at 10m/s and has 40000J of Kinetic energy?

A

Work = energy transferred = 40000J of heat to the brakes and tires.

19
Q

An 800kg car is traveling at 10ms^-1 with 40000 J of energy when the brakes are applied. It stops in 8m. What is the average force excerted by the brakes?

A

Work = Fd Therefore F = Work / d

F = 40000J / 8m = 5000N

20
Q

When Work is applied against frictional forces which is the main energy transferred?

A

Heat

21
Q

Why do we always show the formula when making calculations?

A

Marks can be gained for the correct formula even if the answer is wrong.

22
Q

What unit is Force measured in?

A

Newtons, N

23
Q

What unit is used to measure distance?

A

Metres, m

24
Q

What units is used for Work?

A

Joules, J

25
Q

Name the units of this formula E^K = ½mv^2

A

E^K is Kinetic energy, m is mass, v is velocity or speed

26
Q

What is the formula to calculate Power?

A

P = E/t Power = Energy / time

27
Q

What is Power?

A

The rate of doing Work or how quickly energy is transferred

28
Q

A ball has a mass of 0.1kg is dropped from a height of 1.5m. Assuming all the E^P is turned into E^K. How could you calculate the speed a ball would be falling at the moment before it hits the ground?

A

First calculate E^P = mgh, then because all E^P will be converted to E^K just before it hits the ground use ½mv^2 to calculate v

29
Q

Energy in battery contains of what form of energy?

A

Chemical potential

30
Q

A ringing bell is an example of what form of energy/energies?

A

Kinetic and sound

31
Q

Food is contains what form of energy?

A

Chemical potential

32
Q

A stretched rubber band contains what form or energy?

A

Elastic potential

33
Q

What energy transfers take place while a TV is on?

A

Electrical to heat, light and sound

34
Q

What energy transfer takes place in an iron

A

Electrical to heat

35
Q

Describe the energy transfers that happen as someone parachutes to earth?

A

E^P decreases as E^K until terminal velocity is reached.

Mechanics (2 decks)

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