Energy Resources and Energy Transfers
6 marks · NormalA student of mass 45 kg runs up a staircase that is 3 meters high in 8 seconds.
Calculate the change in gravitational potential energy (GPE) of the student.
Calculate the average power generated by the student while running up the stairs.
State the correct unit for power.
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) 1350 J
(b) 168.75 W
(c) watt (W)
Common mistakes: Forgetting to use g = 10 N/kg
Show mark scheme and worked solution
Marking points
M1 (a) · 1 mark · Substitute correct values into GPE = mgh. (follow-through)
A1 (a) · 1 mark · Correct calculation: 45 x 10 x 3 = 1350 J.
M2 (b) · 1 mark · Uses power = work / time. (follow-through)
M3 (b) · 1 mark · Substitute GPE value and time: 1350/8 (follow-through)
A2 (b) · 1 mark · Correct calculation: 168.75 W.
B1 (c) · 1 mark · Gives correct unit of power (watt or W).
Worked solution
a) GPE = m × g × h = 45 kg × 10 N/kg × 3 m = 1350 J
b) Power = work done / time taken = 1350 J / 8 s = 168.75 W
c) The unit of power is watt (W).