Anonymous

# 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.

Relevance

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.

• 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 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