A physics-power question?

Question

1. An energy-efficient light bulb, taking in 28 W of power, can produce the same level of brightness as a conventional light bulb operation at power 100 W. The lifetime of the energy-efficient bulb is 10 000 h and its purchase price is 45 dollars, whereas the conventional bulb has lifetime 750 h and costs 0.42 dollars. Determine the total savings obtained by using one energy-efficient bulb over its lifetime as opposed to using conventional bulbs over the same time interval, Assume an energy cost of 0.2 dollars per kilowatt-hour.

2. One Calorie in nutrition is one kilocalorie, defined as 1 kcal = 4186 J. Metabolizing 1 g of fat can release 9 kcal. A student decides to try to lose weight by exercising. He plans to tun up and down the stairs in a football stadium as fast as he can and as many times as neccessary. Is this plan in itself a practical way to lost weight? To evaluate the program, suppose he runs up a flight of 80 steps, each 0.15 m high, in 65 s. For simplicity, ignore the energy he uses in coming down (which is small). Assume that a typical efficiency for human muscles is 20%. This statement means that when your body converts 100 J from metabolizing fat, 20 J goes into doing mechanical work (here, climbing stairs) and the remainder goes into extra internal energy. Assume that the student's mass is 75 kg. a) How many times must the student run the flight of stairs to lose 1 kg of fat? b)What is his average power output, in watts as he runs up the stairs?

Answer 1

W means Joule /s

Hence energy saving per second by using energy efficient bulb is 100-28 = 72 W

Savings per watt W is 0 = 0 .2 dollars / kh

Savings for 72 watt =14.4 dollars / kh



For 10 000 h = 10 kh the saving is 10 k h *14.4dollars / kh = =144 dollars



There is a loss in purchase cost by an amount 44.58 dollars

Hence net savings is 144 dollars - 44.58 = 99.42 dollars



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1 kcal = 4186 J.

1 g of fat can release 9 kcal

80 steps, each 0.15 m high, in 65 s.

efficiency for human muscles is 20%

mass is 75 kg.



a) How many times must the student run the flight of stairs to lose 1 kg of fat?

b)What is his average power output, in watts as he runs up the stairs?

Energy lost per time = mgh = 75*9.8*80*0.15 J = 75*9.8*80*0.15 / 4186 kcals

Energy lost in N time = N * 75*9.8*80*0.15 / 4186 kales



Input energy = { N * 75*9.8*80*0.15 / 4186} * 100 / 20 k cals = 10.54 N kcals



9000 kcal release 1 kg of fat



10.54 N k cals = 9000



N = 854 time s

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Answer 2

Beware of "fat-free" or "zero trans fats" foods as you could be trading fats for huge degrees of sugar or sodium.

Answer 3

Increase crazy and also parmesan cheese for you to salad

Answer 4

Go walking regular 35 mins every day

Answer 5

Ok personally I don't think psychic powers exist. BUT! Just try concentrating really hard to use your psychic powers. Practice every day. I guess it would be like working out. The more you practice, the better you will get. And experiment to see what else you can do.

Answer 6

Total cost (TC) = Purchase Cost (PC) + Running Cost (RC)



For efficient bulb over 10000 hrs

RC = (10000hr * 28W / 1000 Wh/kWh) * $0.2 / kWh = $56.00

PC = 1 bulb = $45

TC = $45 + $56 = $101.00



For conventional bulb over 10000 hrs

RC = (10000hr * 100W / 1000 Wh/kWh) * $0.2 / kWh = $200.00

PC = 10000/750 bulbs = 13.3 bulbs @ $0.42 ea = $5.60

TC = $5.60 + $200 = $205.60



Total Savings = $205.60 - $101 = $104.60



Call it $105 especially if you allow for 14 conventional bulbs!

Answer 7

Identify the emotional triggers that make you seek unhealthy comfort food. Picture your goal weight so when a trigger strikes to assist you resist temptation.

Answer 8

It's likely you're eating too fast. Try holding a conversation while wearing a meal so you're not really gulping down more than you have to feel full.

Answer 9

Use a dash of cinnamon to give fruits such as bananas as well as melons a richer dessert feel devoid of the sugar.

Answer 10

Identify the emotional triggers that connect you with seek unhealthy comfort food. Picture your goal weight the next time a trigger strikes to allow you to resist temptation.

Answer 11

have a 40 2nd break down the middle of your meal consider just how eager an individual still are generally before acquiring here we are at the fish

Answer 12

People who regularly weigh themselves and record their progress in a journal will probably lose weight.

Answer 13

Start studying about fitness/nutrition textbooks

Answer 14

take slim protein as well as fruit and vegetables