Chemistry! I have no idea where to begin! Please Help!?

A piece of chocolate cake contains about 400 Calories (food). How many 8-inch steps (expressed to 2 significant figures) must a 180-lb man climb to expend the 400 Cal from the piece of cake?

P.E. = mgh; m = mass; g = acceleration due to gravity 9.8 m/s2; h = height.

(Hint – remember the derived units for a joule.)

Update:

I got 10. but for some reason it's wrong. I'm not sure why. I tried putting "10." "10" "1E1" "1 E 1" but none of it was right.

Update 2:

correction to the last two inputs "1.0E1" "1.0 E 1"

2 Answers

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  • 8 years ago
    Favorite Answer

    First off I would convert calories into joules (1 Calorie = 4.18 Joules)

    400*4.18 = 1672J

    Then I would convert inches into meters (1 inch = 0.0254 meter)

    8*0.0254 = 0.2032m

    Then I would convert pounds into kilograms (1 pound = 0.453592 kilogram)

    Then you set up the equation

    Amount of Energy from the cake = PE = mgh

    1672 = 81.6466*9.81*0.2032*x (x = amount of 8-inch steps)

    Solve for x...and you get 10.273 ---sig figs--->10. steps. It's important that the "." is there since 10 has only 1 sig fig, and since 10.0 has 3 sig figs.

    Source(s): I was an AP Physics B student
  • 8 years ago

    This is a great example of why the metric system is way better especially for science stuff

    a regular calorie of energy = 4.184 J

    BUT a calorie isn't always just a calorie ... like when it comes to chocolate cake (or any food )

    a single food calorie is actually 1000 regular calories ... so your answer is 1/1000 of the actual answer:

    so 400 food calories = 400 x 1000 x 4.184 = 1673600 J

    so 1673600 = mgh

    1673600 = 180 lb x [1 kg / 2.2 lb] x 9.8 h

    h = (1673600 x 2.2) / (180 x 9.8)

    h = 2087 m

    Now 8 in = 8 in x [2.54 cm / in] x [1 m / 100 cm] = 0.2032 m

    Number of steps = 2087 / 0.2032

    Number of steps = 10271 = 10000 (to 1 sig fig) ... [b/c the least number of sig figs in the given data is 1]

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