1) What does the 1st law of thermodynamics state? a) Energy cannot be created but can be destroyed. b) Energy can be created or destroyed in any process. c) Energy cannot be created or destroyed, only transferred or transformed. d) Energy can only be conserved in mechanical systems. 2) True or False? The total energy input to a mobile phone is greater than the total energy output. a) T b) F c) huh?! d) 3) True or False? The total energy output of a washing machine is greater than the total energy input. a) T b) F 4) The total energy input to a wood fire is equal to the total energy output. a) T b) F 5) Calculate the missing energy value X for the diagram shown. a) 500J b) 1000J c) 0J d) 250J 6) Calculate the missing energy value X for the diagram shown. a) 0J b) 100J c) 180J d) 20J 7) Calculate the missing energy value X for the diagram shown. a) 0J b) 700J c) 300J d) 2000J 8) "In a wood fire, 70% of the chemical energy in wood is changed to thermal energy. The remaining energy is changed to light and waste chemicals. Calculate the percentage of chemical energy in the wood that is changed to light and waste chemicals." a) 20% b) 15% c) 30% d) 10% 9) "In an oil-burning power station, 55% of the chemical energy in the oil is changed to thermal energy, and 10% is used in the power station. The remainder is changed to electrical energy. Calculate the percentage of chemical energy in the oil that is changed to electrical energy." a) 55% b) 35% c) 45% d) 90% 10) Sofia has an LED flashlight that uses 18J of electrical energy. 7J of the electrical energy is wasted as thermal energy. Sofia says that 12J of the electrical energy is changed to light. Explain whether Sofia is correct or not. a) Sofia is correct because 12J of electrical energy is used for light, as she mentioned. b) Sofia is partially correct. She correctly identified that not all the electrical energy is used for light, but the correct value is 11J, not 12J. c) Sofia is incorrect. Only 7J of electrical energy is used for light, not 12J. d) Sofia is mostly correct. Although the correct value is 11J for the energy used for light, her answer is close enough to be considered correct.

Y9 3.3 Conservation of Energy CC

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