Consider the energy we use everyday in routine tasks, where that energy comes from, and where it goes. When you walk up a hill you overcome the force of gravity to raise yourself higher against the force of Earth's gravity. It does not matter what the slope of the hill is, only how much farther you are from Earth's center when you are done. The work done is against gravity which is always vertical so only the height counts. Take a typical human mass of 70 kg (roughly 154 lb of gravitational pull or weight) and a hill 30 meters high. That's approximately 9 stories up, so the equivalent energy would be needed to go up 9 floors on a building stairway.

1. How much energy in joules is needed to climb up?
2. What is your potential energy at the top?
3. How many "food calories" or kilocalories (1 calorie is 4.18 j) did you use to make the climb?
4. What total work was done against the force of gravity? If you ate an original Krispy Kreme glazed donut afterward with 190 food calories, will you gain or lose as a result?
5. Walking on mostly level ground obviously consumes energy (50 food calories per kilometer). Where did that energy go, and why is this, even when no net work is done in the physics picture of force and distance?
6. It is often said that it is harder coming down than going up. If you were to raise 70 kg up 30 meters you clearly do work to move it out of the potential energy well it is in from Earth's gravity. If you suddenly release it to fall, that energy is changed to its kinetic energy such that when it meets the floor the velocity it has acquired results in net zero energy energy change. Why do we do "work" on ourselves to walk back down? It's even more obvious after a day hike to and return from a mountain -- say to the ridges of the Smokey Mountains to see autumn foliage from an accessible campground.

Provide a clear explanation of your answers.

By the way, this average mass is taken globally and it would apply to a European, but Americans average closer to 180 lbs weight.

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To calculate the energy needed to climb up a hill we can use the formula for gravitational potential energy Energy needed to climb up The gravitational potential energy is given by the equation PE m g ... View the full answer