1.1: Energy Changes in a System Flashcards

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1
Q

What is the equation for kinetic energy? Give units.

A

1/2m(v2)

Ek = 1/2 * Mass * (Velocity)2

J = 1/2 * kg * m/s

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2
Q

What is the equation for gravitational potential energy?

Give the units.

A

Ep = mgh

Energy = Mass * Gravitational field strength * Height

J = kg * N/kg * m

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3
Q

Define the “Specific Heat Capacity” of a substance.

A

The amount of energy needed to raise the temperature of 1 kg of a substance by 1°C

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4
Q

State the units for Specific Heat Capacity

A

J/°C/kg

Joules/Degrees Celsius/Kilogram

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5
Q

What is the definition of “Power”?

A

The rate at which energy is transferred (or rate at which work is done)

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6
Q

State TWO equations for power.

Give the units.

A
Power = Energy transferred / Time 
Power = Work done / Time 

Energy - J
Work done - J
Time- s
Power - W

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7
Q

Two motors lift the same mass through the same height. Motor A does this in half the time of Motor B. Which dissipates the most power?

A

Motor A

The energy transferred is the same but the time taken is less (P=E/t)

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8
Q

Describe the energy changes involved in when a ball is thrown upwards and then returns to its starting position.
Ignore air resistance.

A
  • Upwards: KE is converted to GPE
  • Peak: Maximum GPE, zero KE
  • Downwards: GPE is converted to KE
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9
Q

Describe the energy transfers for a bungee jumper.

A
  • When falling, GPE is is converted to KE of jumper
  • As the cord tightens, KE is converted and stored as EPE (elastic potential)
  • At lowest point, the jumper’s initial GPE equals the EPE stored in the chord
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10
Q

Explain why a bungee jumper slows down once the cord begins to stretch.

A
  • KE decreases since it’s converted to EPE

- Since KE is proportional to (velocity)2, as KE decreases, so does velocity

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11
Q

Give examples of chemical energy stores.

A
  • Food
  • Fuel (e.g. wood, coal, petrol)
  • Batteries
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12
Q

State 4 different stores of energy

A
  • KE
  • GPE
  • EPE
  • Chemical energy
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