The method and the results are on the energy efficiency lab. Do the analysis yourself first, then check the answers below.
Quick answer: Efficiency is the fraction of the total input energy that becomes useful output: efficiency = useful output ÷ total input, often shown as a percentage. These answers go with the Physics 9-10 lab on energy efficiency: the graph, the calculations, the uncertainties and the conclusion explained, for all 7 analysis questions.
The model answers use the sample table. Your own results will differ, but the order of the surfaces should be the same. Always show the equation, the substitution and the final result with its unit, and explain where the wasted energy goes.
Level: Physics grades 9-10 (GCSE · IGCSE · O Level · Class 9-10) · Curriculum: GCSE P1, HS-PS3-4
GPE = m g h = 0.058 × 9.8 × 1.00 = 0.568 J (0.5684 J).
Question 2 Concrete result
Energy returned = 0.568 × 0.58 = 0.330 J. Energy wasted = 0.568 − 0.330 = 0.239 J (about 0.24 J).
Question 3 Where does the energy go?
Sound (the bounce is audible) and thermal energy, because the ball and the surface warm very slightly as they deform. Sound and thermal energy.
Question 4 Rank the surfaces
Concrete (58 %) > wooden floor (52 %) > carpet (38 %) > sand (12 %). Hard, rigid surfaces return more energy; soft surfaces such as carpet and sand deform and absorb more energy as thermal energy.
Question 5 Predict a second bounce
Second rebound height = 0.58 × 0.58 × 1.00 = 0.336 m, so about 0.34 m.
Question 6 Reading uncertainty
Concrete: 0.02 ÷ 0.58 × 100 = 3.4 %. Sand: 0.02 ÷ 0.12 × 100 = 17 %. The sand result is less reliable because the uncertainty is a larger fraction of the value.
Question 7 Improve the lab
Any two: use slow-motion video for the reading; repeat five times and average; use a ball of the same temperature; release without spin; use a long, vertical, well-lit rule; a second observer at the same level as the top of the bounce. Two justified improvements are enough.
