12032021 Energy Calculations Objective To demonstrate that forces

12/03/2021 Energy Calculations Objective • To demonstrate that forces transfer energy by doing work and that power is the rate of transfer of energy in a system.

Codebreaker Work out the key words from these combinations! Example: 36 E 74 Y = ENERGY 1. 9288 2. 9675 3. 5685 E 4. 769 E 7 5. 96 R 5 366 E 6. 545692 T 8 468 R

Were you successful? 1. 9288 = WATT 2. 9675 = WORK 3. 5685 E = JOULE 4. 769 E 7 = POWER 5. 96 R 5 366 E = WORK DONE 6. 545692 T 8 468 R = KILOWATT HOUR Key words energy joule kilowatt hour power watt work done

Work Done The work done is the amount of energy required to move an object by a certain amount. Work Done = Force x Distance (J) (N) (m) Worked Example If a box is pushed 10 m along a floor with a force of 50 N, calculate the work done? Work done = F x D = 50 x 10 = 500 J Example If a box is pushed 5 m along a floor with a force of 20 N, calculate the work done? Work done = F x D = 20 x 5 = 100 J

Work Done The work done is the amount of energy required to move an object by a certain amount. Work Done = Force x Distance (J) (N) (m) Example A pupil jumps 1. 2 m in the high jump, they have a mass of 60 kg and a weight of 600 N, calculate the work done? Work done = F x D = 600 x 1. 2 = 720 J

Power The power is the rate of transfer of energy in a system. What is the rate? An amount in a given time. The power is the energy used in a given time. Power = Energy ÷ Time (Watt) (Joule) (Sec. ) What is the unit of energy? What is the unit of time? Watt is the unit of power. Example A lightbulb uses 400 J of energy in 10 s. Calculate the power of the bulb. P = E ÷ T = 400 J ÷ 10 S = 40 W

Calculate Your Power Work Done = Force x Distance Power = Energy ÷ Time You have one minute to lift a 1 kg mass (10 N) up off the desk to a height of 50 cm and lower it back down. You should do this as many times as possible within the minute. Calculate the total work done (number of times lifted × force × height). Calculate your power. Compare your power with other members of the class.

Energy Power = Energy ÷ Time We can rearrange the formula to find the energy: Energy = Power x Time Example If a 40 W lightbulb is on for 1 hour, how much energy does it use?

Homework Complete question 2 in your book.

Which lightbulb would you choose?