How many slices of pizza must you eat to walk for 1.5 hr at a speed of 5.0 km/hr

[marfair]

Homework Statement

Assuming a typical efficiency for energy use by the body, how many slices of pizza must you eat to walk for 1.5 hr at a speed of 5.0 km/hr? (Assume your mass is 68kg.) We know that
the energy content in ONE slice of pizza is 1260 kJ and the metabolic power of this activity is 380 W.

Homework Equations

Delta t (change in time) = Delta E (energy)/P(power)
Delta x = v(speed)*delta t (time)

The Attempt at a Solution

I started by calculating delta x, which is 7.5 km total.
I then tried to solve for the change in Energy by taking the power 380 and multiplying it by the time 5400 s (1.5 hr). Since ONE slice is 1260 kJ I thought that I would only need 2 slices but this answer is incorrect. I suppose I would need to first find how much energy it takes to walk at this pace for that amount of time and then compare it to the amount of energy in once slice of pizza. This question is for an extra point so it is not necessary that I do it, but I would like help so that I may figure it out for myself. Any help would be appreciated.

 

[Borek]

Your initial approach seems to be correct (that is ignoring delta x, no idea what you mean by that). Perhaps they want you to give more precise answer (ie not whole slices).

And you know, this is hardly advanced physics...

 

[Mitchellsone]

You have to remember that the human body has 25% efficiency. Therefore divide 1260 by 25% which will give you the amount of energy your body will use from a slice of pizza. Then take whatever answer you get for amount of needed energy (W x T in sec.) and divide that by the amount of energy your body actually uses from a slice of pizza.

 

[willem2]

You have to remember that the human body has 25% efficiency. Therefore divide 1260 by 25% which will give you the amount of energy your body will use from a slice of pizza. Then take whatever answer you get for amount of needed energy (W x T in sec.) and divide that by the amount of energy your body actually uses from a slice of pizza.

I think the efficiency is already factored in the 380W needed for a 68kg person to move at 5 km/hr. That amount of net power/weight will get you close to world record marathon speed.

 

[paranormal]

To accurately answer this question, we need to consider the energy expenditure of walking at a speed of 5.0 km/hr for 1.5 hours. This can be calculated using the formula P = m x g x v, where P is the power, m is the mass, g is the gravitational acceleration, and v is the walking speed. For a 68 kg individual walking at a speed of 5.0 km/hr, the power expended would be approximately 292 watts.

Next, we can calculate the total energy expenditure by multiplying the power by the time walked, which is 1.5 hours or 5400 seconds. This gives us a total energy expenditure of 1576800 joules.

Now, we can compare this to the energy content of one slice of pizza, which is 1260 kJ or 1260000 joules. This means that one slice of pizza would not provide enough energy to sustain walking at a speed of 5.0 km/hr for 1.5 hours.

To determine how many slices of pizza would be needed, we can divide the total energy expenditure by the energy content of one slice of pizza. This gives us a total of approximately 1.25 slices of pizza.

However, it's important to note that this calculation is based on a typical efficiency for energy use by the body. Individual metabolic rates and energy requirements may vary, so the number of slices of pizza needed may differ for each person. Other factors such as the type of pizza and individual dietary needs should also be considered.