Your Stair-Climbing Power (Groups of 3)

Transcription

1 Name Your Stair-Climbing Power (Groups of 3) Safety First! Be very careful when climbing stairs. Do not run up the stairs, but walk at a rapid rate, and hold onto the handrails. If you become tired, out of breath, or experience any other symptoms of discomfort, do not continue with the procedure, If you are unable to climb stairs for health reasons, tell Mr. Bean and participate by timing another student who is able to do so. Skills Predict; Measure; Record data; Calculate; Cooperative learning; Compare and contrast; Infer Background Information Work equals force times the distance through which the force acts. Force is expressed in Newtons (N) and distance is expressed in meters (m). Work is expressed in Newton-meters (N-m), or joules (J). The rate at which work is done is called power. Power equals work time. If work is in joules (J) and time is in seconds (s), power is expressed in joules/second (J/s). One J/s is the same as 1 watt (1 W), a unit named after British scientist James Watt, the inventor of the steam engine. To find out how the power of his engine compared to that of a horse, Watt measured how fast an average horse could do work. He found that answer and expressed the amount of work performed per second as horsepower. One horsepower, expressed in modern metric units, is equal to 746 J/s or 746 W. Questions to consider 1. How much power do you use when climbing stairs? 2. How many times do you have to climb the stairs to lose 1-pound of weight? Goals In this investigation, you will measure the time it takes to climb a set of stairs. Using this time and your weight, you will be able to calculate your power output & possibly calculate weight-loss. Prediction Carefully read the investigation before starting your prediction. Predict how your power output compares to that of an average horse. Give your prediction in fraction or decimal form. Remember to give the reasons for your prediction. Materials Metric ruler Stairs (at least 1 flight high) Stopwatch or watch that indicates seconds Procedure 1. Measure1- person in the group to be the test subject.

2 2. Use the bathroom scale to weigh the subject. Convert pounds to Newtons by multiplying pounds by Measure the height of one stair step, in centimeters. Convert to meters by dividing by 100, and record the result. 4. Count the number of steps you will be climbing. Multiply this by the height of a step to find the total height, in meters. Record this number. 5. Climb the stairs as quickly as you can without running, while your partner times you. Record the time in seconds (and tenths of a second, if a stopwatch is used). CAUTION: Be careful. Hold onto the hand rails. 6. Record data after resting a few minutes, carry out a second climb by repeating procedure step 4. Rest again, and carry out a third climb. Average the three times and record this number. Then change role with your partner and repeat the procedure. Data Table Weight, Distance, and Time Information Weight in Newtons (N) Height of one step (m) Number of steps Total height of stairs (m) Time of Climb 1 (s) Time of Climb 2 (s) Time of Climb 3 (s) Average Time (s) TEST SUBJECT: Observations 1. Were the three climbing times roughly the same, or did they vary considerably? 2. Did the test subject feel as if he/she exerted the same effort on each climb? Explain. Analysis

3 1. Calculate your work in climbing the stairs. Express your answer in Joules. Show your work. Work = (weight in Newtons = Force) x (Total height of stairs = Distance) = Joules 2. Calculate your power output in each climb. Express your answer in Watts. Show your work. Power = Work (from above) Time Climb 1 = Climb 2 = Climb 3 = Average power output for all three climbs = If you had climbed more slowly, how would the work have been affected? How would the power output have been affected? Explain your answer. Calculate your horsepower. To do so divide the average power output you calculated in watts, by the 746, the number of watts in 1 horsepower.

4 Use the conversion, 1-pound = 14,644 kj to estimate how many times the test subject would need to climb the stairs to lose 1-pound. Show work below. Reference: Physics Stair Post-Lab Questions Spring 2013 Multiple Choice (1pt) Identify the choice that best completes the statement or answers the question. 1. Power is defined as the a. force on an object divided by the time the force acts. b. work done times the time taken to do that work. c. work done on an object divided by the time taken to do the work. d. distance divided by the time taken to move that distance. e. force on an object times the distance the object moves. 2. The unit of power is the a. newton. b. meter. c. joule. d. second. e. watt. 3. Which requires more work: lifting a 70-kg sack vertically 2 meters or lifting a 35-kg sack vertically 4 meters? a. Lifting the 70 kg sack b. Lifting the 35 kg sack c. Both require the same amount of work. 4. How many joules of work are done on a box when a force of 25 N pushes it 3 m? a. 1 J b. 3 J c. 8 J d. 25 J e. 75 J

5 5. How much power is required to do 40 J of work on an object in 5 seconds? a. 0 W b. 5 W c. 8 W d. 40 W e. 200 W 6. How much work is done on a 60-N box of books that you carry horizontally across a 6-m room? a. 0 J b. 6 J c. 10 J d. 60 J e. 360 J 7. How much work is done on a 20-N crate that you lift 2 m? a. 0 J b. 1 J c. 2 J d. 20 J e. 40 J 8. How much power is expended if you lift a 60 N crate 10 meters in 1 second? a. 0 W b. 6 W c. 10 W d. 60 W e. 600 W True/False (1pt) Indicate whether the statement is true or false. 9. The unit of power is the watt. 10. The rate at which work is done is called power. Problem Show work and correct units (3pts) 11. What is the work done in raising a 20-kg block 5 m vertically? 12. Is it possible to determine the power expended when a barbell is raised 5.0 m in 2 s? Why or why not? Power = work/time = (Force. distance)/time = (mass. gravity. distance)/time

6 13. What amount of work can a 600-W motor do in 4 minutes? 14. A couch potato might consume 7 million J of energy in a day. What is this rate of energy consumption in watts? 15. A 30-kg girl runs up the staircase to a floor 5 m higher in 8 seconds. What is her power output?