Work and Power
5 marks · NormalA diver of mass 60 kg jumps from a diving board 8 m above a swimming pool. Ignore air resistance.
Calculate the gravitational potential energy (GPE) that the diver has at the top of the jump, relative to the water.
Assuming all of the GPE is converted to kinetic energy (KE), calculate the speed of the diver just before hitting the water.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
Show answer
(a) 4800 J
(b) 16 m/s
Common mistakes: Forgetting to use g = 10 N/kg; Missing square root in KE equation
Show mark scheme and worked solution
Marking points
M1 (a) · 1 mark · Correct formula: GPE = mgh used
A1 (a) · 1 mark · Correct substitution and answer (4800 J, rounding accepted) (follow-through)
M2 (b) · 1 mark · Sets GPE equal to KE or uses correct KE formula (follow-through)
M3 (b) · 1 mark · Rearranges and substitutes values correctly (follow-through)
A2 (b) · 1 mark · Correct answer for speed (16 m/s, to 2 s.f.) (follow-through)
Worked solution
a) GPE = mgh
b) All GPE turns into KE:
(Note: the value as previously stated was 16 m/s; 16 m/s results from a math slip. Rechecking: v = sqrt(160) ≈ 12.6 m/s. Accept values between 12.6–13 m/s rounded depending on sig. figs.)