Power
4 marks · HardA bungee jumper leaps from a bridge, attached securely to an elastic cord. Describe in detail how energy is transferred between stores from the moment the jumper steps off the platform until the lowest point of the jump, including where energy is not conserved as useful energy. Refer to named energy stores and describe at least three distinct transfers in your answer.
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Also accept: thermal energy due to air resistance or in the cord
Common mistakes: Omitting mention of elastic energy; Failing to state where energy is dissipated; Mixing up energy transfers and stores
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Marking points
M1 · 1 mark · States energy initially as gravitational potential energy (GPE).
M2 · 1 mark · Describes transfer from GPE to kinetic energy (KE) as the jumper falls.
M3 · 1 mark · Describes transfer from kinetic to elastic potential energy as the cord stretches.
M4 · 1 mark · Identifies energy not conserved as useful energy, such as dissipation as heat or sound.
Worked solution
When the bungee jumper steps off the platform, their energy is almost entirely gravitational potential energy (GPE) due to their height above the ground. As the jumper falls, this GPE is transferred to kinetic energy (KE) as their speed increases. As they near the end of the cord, the elastic cord stretches, converting the kinetic energy into elastic potential energy stored in the stretched cord. As the jumper slows to a stop at the lowest point, most of the kinetic energy has been transferred to elastic potential energy. Some energy is not conserved usefully: energy is dissipated due to air resistance and internal friction in the cord, which is transferred as heat and sound to the surroundings.