The method and the results are on the work and power lab. Do the analysis yourself first, then check the answers below.
Quick answer: Work is the energy transferred when a force moves an object, found from W = F × d and measured in joules. These answers go with the Physics 9-10 lab on work and power: the graph, the calculations, the uncertainties and the conclusion explained, for all 7 analysis questions.
The model answers use the sample results from the table. Your measurements will differ, but the same pattern should appear: constant work and power that rises as the time falls. Show the equation, the substitution and the unit each time.
Level: Physics grades 9-10 (GCSE · IGCSE · O Level · Class 9-10) · Curriculum: HS-PS3-1
W = m g h = 48.0 × 9.8 × 3.85 = 470.4 × 3.85 = 1811 J, so about 1810 J.
Question 2 Calculate a power
P = W ÷ t = 1811 ÷ 7.8 = 232.2, so 232 W.
Question 3 Same work, different power
Work depends only on the weight and the height gained, W = m g h, which do not change. Power is work divided by time, so a shorter time gives a larger power.
Question 4 Plot and interpret
The values of 1 ÷ t are 0.109, 0.128, 0.179 and 0.256 s⁻¹. The graph is a straight line through the origin because P = W × (1 ÷ t). The gradient equals the work, about 1810 J.
Question 5 Compare with a lamp
Run: 464 W ÷ 100 W = about 4.6, so she could light four lamps fully (and a fifth dimly). The body transfers energy at a rate similar to several bulbs.
Question 6 Uncertainty
0.3 ÷ 3.9 × 100 = 7.7 %. The percentage uncertainty in power is about the same, 7.7 %, because P is proportional to 1 ÷ t. The fastest trial is the least precise.
Question 7 Improve the lab
Any two: use light gates or a video to time more precisely; repeat each trial three times and average; measure step height at several steps; use a longer staircase to reduce the percentage uncertainty in t. Assumption: only the gain in gravitational potential energy is counted; the kinetic energy of the climber and the energy to move the legs are ignored.
