Energy changes in a system Flashcards

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1
Q

What is the equation for elastic potential
energy? Give SI units for all quantities
involved.

A

½ k x2
½ x Spring Constant x (Extension)²
Energy (J), Spring Constant (N/m), Extension(m)

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2
Q

What is the equation for gravity potential
energy? Give SI units for all quantities
involved.

A

mgh
Mass x Gravitational Field Strength x Height
Energy (J), Mass(kg), Gravitational Field Strength (N/kg),
Height (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 kilogram of a
substance by 1 degree Celsius.

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4
Q

State the units for Specific Heat
Capacity.

A

J/°C/kg
Joules/Degree 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 SI
units for all quantities involved.

A

power = energy transferred/time
power = work done/time
Energy (J), Work Done (J), Time (s)

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7
Q

What is the unit of power?

A

Watt (W)

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8
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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9
Q

Describe the energy changes involved
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
KE (Kinetic Energy), GPE (Gravitational Potential Energy

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10
Q

Describe the energy transfers for a
bungee jumper.

A

● When falling, the GPE is converted to KE of
jumper
● As the cord tightens, KE is converted and
stored as Elastic Potential Energy (EPE)
● At lowest point, the jumper’s initial GPE
equals the EPE stored in the cord
www.pmt.education
Explain why a bungee jumper slow

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11
Q

Give examples of chemical energy
stores.

A

● Food
● Fuel (eg. wood, coal, petrol)
● Batteries

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12
Q

State 4 different stores of energy.

A
  1. Kinetic Energy
  2. Gravitational Potential Energy
  3. Elastic Potential Energy
  4. Chemical Energy
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