5.5 - Riding your bike up a hill
Picture yourself riding a bike up a hill, resting for a bit, and then coasting down the other side. As you Work to get up the hill, you gain potential energy. As you coast down the other side, that potential energy is converted to kinetic energy.
The work you originally did to get up the hill is the total amount of energy in the system. All of the PE and KE must add up to this no matter where you are on the hill. Like the pendulum, there are two very special spots where all of the energy is either PE or KE.
At the top of the hill, before you begin to descend, you only have potential energy. Since there is no motion yet, there is no kinetic energy. This means that the work needed to get up the hill is the potential energy at the top.
Once you have coasted down the hill and are at the bottom, all of the energy is kinetic. Since the bottom of the hill is considered height = 0 m, there is no potential.
If you wanted to stop the bike at the bottom, all that kinetic energy would have to go somewhere. When you pull on the brake lever, this causes rubber brake pads to squeeze the rim of the tire creating Friction which causes the bike to stop. Friction creates Heat and this is the final energy conversion in this example.
The work you originally did to get up the hill is the total amount of energy in the system. All of the PE and KE must add up to this no matter where you are on the hill. Like the pendulum, there are two very special spots where all of the energy is either PE or KE.
At the top of the hill, before you begin to descend, you only have potential energy. Since there is no motion yet, there is no kinetic energy. This means that the work needed to get up the hill is the potential energy at the top.
Once you have coasted down the hill and are at the bottom, all of the energy is kinetic. Since the bottom of the hill is considered height = 0 m, there is no potential.
If you wanted to stop the bike at the bottom, all that kinetic energy would have to go somewhere. When you pull on the brake lever, this causes rubber brake pads to squeeze the rim of the tire creating Friction which causes the bike to stop. Friction creates Heat and this is the final energy conversion in this example.
5.5 Sample Problems
Supplemental Question
How many hamburgers does it take to get to the top of the Prudential Tower?
We have been discussing the ideas of work and energy. When going up stairs, you do work and gain gravitational potential energy. You originally get that energy from the food you eat. Where we have been using the Joule as our energy unit, most people are used to the Calorie (C) when dealing with food.
How many hamburgers would you have to eat to have enough energy to climb to the top of the Prudential Tower?
Some information you may need:
We have been discussing the ideas of work and energy. When going up stairs, you do work and gain gravitational potential energy. You originally get that energy from the food you eat. Where we have been using the Joule as our energy unit, most people are used to the Calorie (C) when dealing with food.
How many hamburgers would you have to eat to have enough energy to climb to the top of the Prudential Tower?
Some information you may need:
- 1 hamburger = 400 Calories (these are Kilocalories)
- 1 Calorie = 1000 calories
- 1 calorie = 4.18 Joules
- Mass of average person = 68 Kg
- Humans are 30% efficient with what they eat. They can only take out 30% of the available energy.
- The height of the Prudential tower is 228 meters.