Tiêu đề 2020 GCE A level H2 Physics 9749 Ans.pdf ✅

8 Note 1: there are 2 ropes so 2 tensions pulling down on the basket. Note 2: upthrust = weight of fluid displaced. Therefore the density of air used should be the density of the surrounding air at 20 °C. Note 3: it is also a common mistake to neglect the weight of the air in the balloon. 2 x Tension + (weight of balloon, basket and air inside balloon) = Upthrust 2 x Tension + (700 x 9.81 + 2800 x 0.898 x 9.81) = 2800 x 1.204 x 9.81 Tension = 770 N = 0.770 kN 9 Rate of useful work done = P = F v = 1600 x 22 = 35200 J s-1 Rate of thermal energy produced by burning fossil fuels = 3.3 x 106 J min-1 = 55000 J s-1 Efficiency = 35200 / 55000 = 64% 10 Centripetal acceleration = r ω2 = r (2π / T)2 = (3.85 x 108 )(2π / (27.3 x 24 x 60 x 60))2 = 2.73 x 10-3 m s-2 11 Period, T = 1 h = 3600 s ω = 2π / T = 2π / 3600 = 1.75 x 10-3 rad s-1 12 1 2 1 2 1 2 Increase in GPE 2 2 Gm m Gm m r r Gm m r           upthrust Tension Tension Weight of balloon, basket and air inside balloon