Anonymous
Anonymous asked in Science & MathematicsMathematics · 1 decade ago

Convert Cal/day to Joules/sec. Help!?

A person who just sits around most of the time needs about 2,000 calories per day. What is that person's average power level in Watts? (This is a unit conversion problem. 2,000 Cal/day = ? Joules/sec)

*I've been working on this stuff for 2 hours and can't seem to figure this one out or find it in the book. My brain may be fried at this point. Help is much appreciated!

Update:

Thanks Thorbard! That is right! I realize I was taking the wrong approach at this. I might need to take a break.

5 Answers

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  • 1 decade ago
    Favorite Answer

    1 day = 24 hours x 60 minutes/hour x 60 seconds/minute = 86400 seconds.

    2000 kCal/day = 2000/86400 = 0.02314 Cal/second

    1 kCal = 4184 J

    So 2000 kCal/day = 0.02314 x 4184 = 96.82 W

    I've assumed that the question meant kCal (food calories) not Cal (thermodynamic calories). If you want to know for the lesser quantity, divide all references by 1000.

  • 1 decade ago

    The method for unit changes is to multiply some quantity with unite by 1, which does not change its value. But the 1 is made up of a numerator in that is some amount of one unit and the denominator is made up of the amount of another unit that expresses an equal amount. Anything divided by the same amount equals 1. You choose the ratio that equals1 so that the units you want to get rid of cancel out with the starting value and the unit you want to replace it with is left behind in its place. There are several definitions of Calorie, so if I use the wrong one, you will have to correct that.

    In this case:

    1 Cal = 4.18 joule so:

    4.18 joule / 1 Cal = 1

    1 day = 24 hours, 1 hour = 60 minutes , 1 minute = 60 seconds,

    so:

    1 day/ 24 hours = 1

    1 hour/ 60 min = 1

    1 min/60 sec = 1

    (2000 Cal/day) * (4.18 joule/1 Cal) = 8360 joules/day

    (8360 joules/day) * (1 day/24 hours) = 348.333 joules/hour

    (348.333 joules/hour) * (1 hour/ 60 min) = 5.80555 joules/min

    (5.80555 joules/min) * (1 minute/60 sec) = 0.096759 joules/sec

    And since we did nothing but multiply by various forms of 1, the result is the same as what we started with, only expressed in different units.

    --

    Regards,

    John Popelish

  • Anonymous
    4 years ago

    Calories To Joules Calculator

  • 1 decade ago

    1 Cal = 4.18400 Joules

    2000*4.18400 = 8368

    seconds in 24 hours = 24*60*60 = 86400

    86400/60 = 1440

    8368/1440 = 5.811 Joules/sec

    Hope this helped

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  • achain
    Lv 5
    1 decade ago

    Use the unit converter:

    http://www.digitaldutch.com/unitconverter/energy.h...

    First convert cal/day in cal/sec, then go to joules/sec

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