Unit 6 Reflection

In this unit of physics, the class was introduced to energy. We learned about work, power, kinetic energy, potential energy, the law of conservation of energy and mechanics. This unit proved to be more technical as we advanced however the concepts are easy to comprehend. 

Guiding Question: Your force is 200n and you climb 5 meters in 2 seconds. how much work is done? How much power did you generate? 

Work is a force that acts on a body. Work is a parallel force and therefore does not work when the two forces are perpendicular. An example of work is someone walking up the stairs. Since the person has a force of gravity pulling them down, and moving upwards, the person must exert a force to go up the stairs. Since the vector arrows are parallel the person is said to be doing work. An example of someone not doing work is a waiter carrying a tray to a table. Although the waiter is carrying the tray he is not doing any work as he walks to the table. Force and distance must be parallel. If the force applied doesn't cause and object to move, than no work is done. An example of this is someone pushing a wall. Although they are applying a large force, the wall doesn't move and therefore no work is done. Work is measured in joules (a newton-meter). The equation for work is:

                                                        work (Joules) = Force (N) x Distance (meters)

Power, is similar to work, by factors in the amount of time. Power is defined as the rate of work produced. This is measured in watts (joules per second). Power is calculated in the equation below:

                                                         Power (Watts) = Work (joules) / Time (Seconds) 

Knowing this information now, we are able to solve our guiding question;

1. Work = force x distance
2. W = 200 x 5
3. W = 1000J
4. Power = work/time
5. Power = 1000/2
6. Power = 500 watts

In order to climb the stairs it would require 1000 joules  Once at the top you would of produced 500 watt in 2 seconds. 

Guiding Question 2: A ball with a mass of 10kg is dropped off a 200m cliff. What is the velocity of the ball right before it hits the ground

Potential energy is the energy stored in an object based on its mass and height. An object has full potential energy at the top of its path when it is not moving. Once the object begins to move this potential energy becomes transformed into a different form of energy. The energy of motion is refereed to as kinetic energy. The Law of Conservation of Energy states that energy can neither be created nor destroyed, only transformed. As the object falls and gains velocity, it also gains kinetic energy. At the end of the objects path, right before it hits the ground, the object has full kinetic energy. Since the potential energy will eventually be transformed into kinetic energy they are measured in joules. To calculate both potential and kinetic energy, physicists have created two formulas:

                                    Potential energy (Joules) = mass(m) x gravity(g) x height(h)

                                    Kinetic energy (Joules) = (1/2) x mass (m) x velocity^2 (m/s)

With the following information we are now able to answer our second guiding question. 

1. Pe = mgh
2. Pe = (10)(10)(200)
3. Pe = 20000J
4. Pe = Ke
5. 20000 = 1/2(10)v^2
6. the answer is 63.24 m/s.

Guiding Question 3: You need to get a heavy box into your truck. Although you only need to lift the box 2m high, the box has a force of 400n. You have a 3m ramp. How much force would it be to push the 400m box up the 3m ramp?

When we think of a machine we think of electronics (car, computer etc.). A machine also exists in physics. A machine can look like a ramp in the picture above. We can use a simple machines to move heavy object and use less force. The ups man uses a ramp because he is able to use less force by covering a larger distance. To solve for the work done in a simple machine we use the work equation. 

1. Work = mass x distance
2. work = 400 x 2 
3. work = 800J
4. f(3) = 800
5. f = 800/3
6. f = 266.66 N

Now if someone tells you that they have a machine that is 100% efficient, you need to correct them. To calculate the efficiency of a machine we use the equation 

                                                          

                                                             Efficiency = workout/work in 

No machine is 100% effective because we live in an imperfect work. Energy is transformed into friction on a molecular level as well as with air particles.