Topic 1 - Energy - 1.1-Energy Changes In A System

Question 1

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

Answer 1

½ m v2
½ x Mass x (Velocity)²
Energy (J), Mass(kg), Velocity(m/s)

Question 2

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

Answer 2

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

Question 3

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

Answer 3

mgh
Mass x Gravitational Field Strength x Height
Energy (J), Mass(kg), Gravitational Field Strength (N/kg),
Height (m)

Question 4

Define the ‘Specific Heat Capacity’ of a
substance.

Answer 4

The amount of energy needed to raise
the temperature of 1 kilogram of a
substance by 1 degree Celsius.

Question 5

State the units for Specific Heat
Capacity.

Answer 5

J/°C/kg
Joules/Degree Celsius/Kilogram

Question 6

What is the definition of ‘Power’?

Answer 6

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

Question 7

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

Answer 7

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

Question 8

What is the unit of power?

Answer 8

Watt (W)

Question 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?

Answer 9

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

Question 10

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

Answer 10

●Upwards: KE is converted to GPE
●Peak: Maximum GPE, zero KE
●Downwards: GPE is converted to KE
KE (Kinetic Energy), GPE (Gravitational Potential Energy)

Question 11

Describe the energy transfers for a
bungee jumper.

Answer 11

●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

Question 12

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

Answer 12

●Kinetic energy decreases since it is
converted to elastic potential energy
●Since KE is proportional to (velocity)²,
as KE decreases, so does velocity.

Question 13

Give examples of chemical energy
stores.

Answer 13

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

Question 14

State 4 different stores of energy.

Answer 14

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