1.1 - Energy Changes in a System

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

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1

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

  • ½ mv2

  • ½ × mass × (velocity)2

  • energy (J), mass (kg), velocity (m/s)

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2

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

  • ½ ke2

  • ½ × spring constant × (extension)2

  • energy (J), spring constant (N/m), extension (m)

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3

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

  • mgh

  • mass × gravitational field strength × height

  • energy (J), mass (kg), gravitational field strength (N/kg), height (m)

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4

Define the “Specific Heat Capacity” of a substance.

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

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5

State the units for Specific Heat Capacity

  • J/°C/kg

  • Joules/Degrees Celsius/Kilogram

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6

What is the definition of “power”?

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

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7

State two equations for power. Give SI units for all quantities involved.

  • power = energy transferred / time

  • power = work done / time

  • energy (J), work done (J), time (s)

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8

What is the unit of power?

watt (W)

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9

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?

  • Motor A

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

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10

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

  • Upwards: KE is converted to GPE

  • Peak: Maximum GPE, zero KE

  • Downwards: GPE is converted to KE

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11

Describe the energy transfers for a bungee jumper.

  • 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

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12

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

  • Kinetic energy decreases since it is converted to elastic potential

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

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13

Give examples of chemical energy stores.

  • Food

  • Fuel (e.g. wood, coal, petrol)

  • Batteries

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14

State 4 different stores of energy.

  1. Kinetic energy

  2. Gravitational Potential energy

  3. Elastic Potential energy

  4. Chemical energy

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