WARM UP: Work and Power Example Problems 1) What is work? (words and formula)

Transcription

1 WARM UP: Work and Power Example Problems 1) What is work? (words and formula) 2) Your mom drops off your lunch in the office and you have to go up the stairs to the office to get it. Are you doing work as you go up the stairs? Why/why not? 3) If you are doing work, how would you find how much work you were doing as you went up the stairs? 4) what is another way to describe work? 5) What is the difference between work and power? Calculations: 6. Calculate the work done by a 52 N force pushing a bottle of nail polish 0.26 m. Formula Setup Final Answer 7. A hedgehog pushes an onion with 5 N of force for 4.5 m. It takes him 3 seconds. What is the power he generates? Formula Setup Final Answer

2 A Powerful Workout Experiment!!! Questions: How does the amount of work you do to walk up the stairs compare when walking quickly vs. walking slowly? How many joules of energy will we use/calories will we burn doing each? How does the amount of power you produce walking slowly up the stairs compare with the amount of power you produce walking quickly up the stairs? Hypotheses: Hey, what s your name? date: Introduction: Work is the transfer of energy. Work is found by multiplying the force exerted on an object by the distance through which the force is applied. So, this is the equation for work: W=. The unit for work is equal to one newton-meter, also known as the: Power is the rate at which energy is transferred from one object to another or converted from one form to another. Power can be found by dividing the work done by the time it takes to do the work. So, this would be the equation for figuring out power: P= The unit for power would be newton-meters per second or /, which is also also known as the If I walk slowly up the stairs, then my work will be than walking quickly up the stairs. If I walk slowly up the stairs, then my power will be than walking quickly up the stairs. PRE-LAB QUESTIONS: 1. When climbing a flight of stairs On each step, what direction is your action force applied by your foot/leg? In what direction is the equal and opposite reaction force applied on you? 2. Which direction do you accelerate/move as a result? 3. Is work being done as you go up a flight of stairs? Why/Why not? 4. How much force does it take to lift your body up a flight of stairs? 5. a) In order to figure out the work that you do while climbing a flight of stairs, what else do you need to know besides the force you are applying?

3 Lab Procedures/Reminders: 1) We will be doing this lab on the stairs by the cafeteria. On our journey there, we need to make sure we are quiet and mature so as to not disturb other classes. They should not even know we are there. If you are having a problem with this, you will be asked to sit in another classroom, or to sit out. 2) When we get to the stairs, we will line up in a single-file line. When in line, you should not be talking, once again, it s important we are not disturbing other classes! 3) We will all complete the Slow walk up the stairs, then we will all do the Fast walk. One person will go at a time, or when Ms. Hall tells you to go. Just before you begin, you will start your timer, then stop the timer when you get to the top of the stairs. REMEMBER YOUR TIME (you can round to the nearest tenth to make it easier). 4) Quietly come down the other side of the stairs (the down stairs side) then hand your timer to the next person in line who needs it, then get back in line. 5) When you are done and you ve gotten both your times, pick up the work, power, and simple machines vocab review x-word from Ms. Hall. Sit near the wall quietly, and start working on this (individually) until everyone else is done.

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5 NAME/DATE/Pd: Page 2: A Powerful Workout Experiment: DATA: Type of Motion SLOW TIME (convert to SECONDS) Height of Each Stair (cm) Total number of Stairs TOTAL Height of Stairs (m) (DISTANCE) QUICK 16cm = m 23 FORCE The force that you applied to lift yourself up the stairs is equal to your weight in Newtons. Convert your weight to Newtons by filling in your approximate weight in pounds into the equation below: = Newtons Tomorrow we will use this information to calculate the amount of work and power we generated. Day 1 analysis questions (day 1): 1. Are you doing the exact same amount of work as everyone else in the class? Why/why not? 2. What variable would effect who would be doing the most amount of work? 3. How could you increase the amount of work you were doing? Decrease?

6 Name: Date: Pd.: DAY 2: A Powerful Workout Experiment Calculate the work and power done for both the quick and slow walks. Show your calculations below. Show all units and box your answer. WORK calculation for SLOW walk: Make sure to show all units! WORK calculation for QUICK walk: Make sure to show all units! POWER calculation for SLOW walk: Make sure to show all units! POWER calculation for QUICK walk: Make sure to show all units! Now, fill in the information in the table below: Slow Walk Quick Walk Force (N) Time (s) Work (J) Power (W) The Effect of the Time on Work and Power Conclusion and Analysis: Use the data to support your answers. 2) How does the amount of WORK compare if you walk quickly up stairs vs. walking slowly up stairs? Why is this the case?

7 3a) Work can also be defined as energy transfer. The unit for work, the Joule, therefore, is really a unit of. Another common unit for energy we see everyday is a unit called the calorie. One nutritional calorie is equal to about 4,200 J. Figure out how many calories (energy) you burned while going up the stairs using dimensional analysis: Your work = J x cal(nutritional) = nutritional calories (approx.) 1 J (Wow! What a great workout! ) 3b)Another unit for energy used is known as the Kilowatt Hour (kwh)*. This is a unit for energy commonly found on your electricity bills and energy-meters at your home. Convert the work you did while going up the stairs to kwh (1 kwh = 3.6 MegaJoules, 1 MegaJoule = 1 million [1,000,000] Joules). Your work = J x MegaJs x kwh = kwh (approx.) 1 J MegaJs 3c) According to the Energy Information Administration of the United States, the average home in Virginia uses 1,117 kwh of energy per month. How does the amount of work you did compare? How many times would you have to go up the stairs to use the same amount of energy as an average house? 1117 kwh = times!!! (your kwh of work).* Yes, The kwh sounds like it should be a unit of power, since in includes the Watt, however, if you think about it, 1W x 1 sec = 1 J, so 1 kwh = 1000W x 3600 sec, or 3.6 megajoules*, which is a unit of energy). 4) How does the amount of POWER compare when you quickly walk up the stairs vs. slowly walking up the stairs? 5) Why is the amount of POWER changed but your WORK stays the same for both situations? 6) What are at least 2 ways you could increase the amount of WORK you are doing as you climb the flight of stairs? How could you actually make this a good workout? 7) What are at least 2 ways you could increase your POWER even more when walking up the stairs?