Question

WILL REWARD MEDAL/ FAN!!((((:
The fuel value of peanuts is 25 kj/ gram. If an average adult needs 2800 kilocalories of energy a day, what mass of peanuts would meet an average adult's energy needs for the day? Assume all of the fuel value of the peanuts can be converted to useful energy.

Answer 1

1 adult's energy requirement = 2800 kc/day

how many kilo calories are required "for the day"?

Answer 2

2800?

Answer 3

yes,

Answer 4

how many joules of energy, is 1 kilocalorie?

Answer 5

4.184

Answer 6

so how many joule of energy is 2800 kilocalories,

i.e. 2800 [kc] x 4.184 [j/kc] =

Answer 7

11715.2 joules?

Answer 8

So , we have a requirement of 11715.2 [ j ] .


And, we know the fuel value of peanuts is 25 [ kj / g ]

Answer 9

yeah

Answer 10

wait a minute

4.184 kilojoules* of energy, is 1 kilocalorie!

Answer 11

so we have 11715.2 [kj ] .

Answer 12

yeah.
how do you set it up?

Answer 13

food value [ kj/g ] = energy [ kj ] / mass [ g ]


so

mass [ g ] = energy [ kj ] / food value [ kj/g ]

Answer 14

mass = 4.184 kj / 25?

Answer 15

oh and then you just divide it and the answer will be in grams?

Answer 16

yeah , what do you get?

Answer 17

doe it seem like a reasonable result?

Answer 18

0.17 grams

Answer 19

is that correct?

Answer 20

wait, a minute

Answer 21

mass of peanuts [g] = 11715.2 [kj ] / 25 [kj/g]

Answer 22

the energy required is the 11715.2 [kj]

Answer 23

468.61 grams?

Answer 24

that feels more correct than the answer I got less than 1 last time

Answer 25

yeah, about half a kilo seems reasonable to me

Answer 26

so basically we just had to convert kilocalories to kilojoules to get the mass?

Answer 27

first, we found the energy required in the time considered (one day)

then we converted the energy from kilocalories to kilojoules

and then from kilojoules, we used the fuel value of peanuts to find the mass of peanuts that provides this energy

Answer 28

Oh, okay. I see how it relates to the problem now. Thanks.

Answer 29

I have one more if you don't mind.

Answer 30

The specific heat of aluminum is 0.902 joule / g x Celsius and that of silver is 0.235 joules / grams x Celsius. You have two spoons of equal masses. One is made of aluminum and other silver. Which spoons would increase in temperature faster in a pot of hot soup? Why?

Answer 31

This one is so hard

Answer 32

Do you think you can help me with this one?

Answer 33

if we look at the units of specific heat capacity, that is \([\frac{\textrm j}{\text g\,°\text C}]\)

Answer 34

yep

Answer 35

the units say the specific heat capacity is: the energy [joules]
to heat a mass [grams] by a temperature [°C]

Answer 36

yeah, i understand that.

Answer 37

so which spoon takes the lesser amount energy transfer to heat up

Answer 38

Would it be the silver? Since 0.235 is less than 0.902 joules? So then it would take less amount for energy to heat?

Answer 39

yep,

from experience, we know that metals are good conductors of heat
[ metals feel very cold on a normal day, or burn us quickly if they are hot and we touch them ]

Answer 40

silver is a 'better' metal than aluminium

more shiny and much better conductor

Answer 41

so the aluminum will be faster to heat up in a pot of hot soup because 0.902 joules is greater than 0.235 joules.

Answer 42

nope the Al takes more energy to transfer temperature

Answer 43

(which takes more time)

Answer 44

wait so the higher the joule, the more energy it requires for it to heat something up?

Answer 45

more to heat it up AND more to cool it down

Answer 46

so silver will increase the temperature faster due to it's smaller joule, which makes the process of heating faster than the alumiunum?

Answer 47

the mass are the same ,

the comparison is the joule to degree ratio

Answer 48

So my answer is going to be
The silver spoon will increase in temperature faster than aluminum since silver has a smaller joule. The higher the number of joules, the more energy it requires to heat up something.

Answer 49

is it okay? should i add anything?

Answer 50

The silver spoon will increase in temperature faster than aluminium spoon, since the masses are the same, and silver has a smaller specific heat than aluminium: The greater the specific heat, the more joules of energy must transfer to the spoon; the more time is required for soup to heat the spoon by a given amount.