ANS OX AQA P1 Rev Guide 1.1 1 elastic potential energy 1.1 2 gravitational potential energy 1.2 1 An isolated system (object or set of objects0 in which no energy enters or leaves the system 1.2 2 An electric current in the wires transfers energy from the chemical store in the torch batteries into increasing the thermal energy store of the surface of where the light waves go. 1.3 1 Joule , J 1.3 2 Work done = force x distance, = 600N x 12m = 7,200 J 1.4 1 The gravitational energy store decreases when an object moves downwards. 1.5 1 Ee = ½ ke2 = ½ x 150 x 0.2 = 15 J 1.6 1 Wasted energy is transferred to warm up the surroundings 1.6 2 Energy can never be destroyed or ‘lost’, it is transferred by heating up the surroundings 1.7 1 Efficiency = (useful Energy ) / (total energy supplied) = 10 / 25 = 0.4 (or 40%) 1.7 2 A more streamlined vehicle will be more efficient. 1.8 1 Wasted energy from a light bulb is transferred to warm up the surroundings using infra red radiation 1.8 2 A toaster will radiate some of the infrared waves away from the bread instead of toasting it. 1.9 1 2.2kW = 2,200W 1.9 2 Power = E/t = 36,000 J / 120s = 300W Q1 Elastic potential energy Q2 Chemical PE store in muscles decreases, gravitational PE store of box increases Q3 Work done = Force x distance = 1500N x 60m = 90,000J Q4 Gravitational PE store increase = mgh = 0.45kg x 9.8N/kg x 3.0m = 13 J (13.2 J) Q5 Chemical PE store in muscles decreases, Elastic PE store in spring increases then decreases. Muscles & and spring increase their thermal energy stores and i.r. waves warm up the surroundings. Q6 The force must move ( in the direction of the applied force) for work to be done Q7 KE = ½ m v 2 = ½ x (50/1000) x (8/100)2 = ½ x 0.05 x 0.0064 = 0.00016 J Q8 Power = E/t = Work done/ t = (Force x distance) / t = (200N x 12m) / 15 s = 160W Q9. Ultimately: Gravitational potential energy store decreases, thermal energy store of surroundings increases Going down: GPE KE elastic energy store Going back up: KE GPE then KE elastic energy store and the process repeats Thermal energy is transferred to the surroundings on each bounce until GPE is reduced to zero Q10 Work done on trolley = Weight of trolley x slope height (which increases trolley’s gravitational PE store) Work done by person = pushing force x slope length (part of the pushing force is friction, so there is an increase in the thermal energy store of the surroundings instead of 100% transfer to the trolley’s gravitational store) Q11 Efficiency = (useful E output) / ( total E Input) = 28 / ( 28 + 42) = 0.4 = 40 % Q12 E= (1/2) ke2 so E / ((1/2) e2 ) = k k = 1.2 / ((1/2) 0.082 ) = 375 N/m