CH6_TalasH

toc =Work, Energy, and Power - Lesson 1= a

What is work?

Work is done on an object when a force acts upon an object to cause a displacement of the object. The Joule is the unit of work which is 1 Newton * 1 meter.

How do you know when there is work?

For there to be work, the displacement must be in the same direction as the force. For example, a waiter carries a tray full of meals above his head; there is horizontal displacement, however the force is applied vertically.

What is negative work?

Sometimes a force acts upon a moving object to hinder a displacement, like when a car is skidding. This means that the force is acting in the opposite direction of motion which makes the angle between d and f 180 degrees.

How do you calculate work?

The following equation must be used to calculate work with the values of the displacement, force, and theta:

When the force is in the same direction as the displacement, theta is 0 degrees. However when its in the opposite direction, its 180 degrees, and when its perpendicular to d, its 90 degrees. = = =Work, Energy, and Power - Lesson 2= a, b, c, d, e


 * A**

What are internal forces?

Internal forces include the gravity forces, magnetic force, electrical force, and spring force

What are external forces?

External forces include the applied force, normal force, tension force, friction force, and air resistance force.

How does work affect mechanical energy?

If the work is negative work, then the object will lose energy. The gain or loss in energy can be in the form of PE, KE, or both, and so tthe work that is done will be equal to the change in mechanical energy of the object.

What are conservative and non-conservative forces?

When forces are capable of changing the total mechanical energy of an object, they are non-conservative. (external forces) Conservative forces are forces that are capable of changing the form of energy without changing the total amount of mechanical energy. (internal forces)


 * B**

How is the quantitative relationship between work and mechanical energy expressed? Here, the mechanical energy can be kinetic or potential energy and so the equation can be re written as: The external force force can be positive or negative depending on the angle.
 * TMEi + Wext = TMEf**
 * KEi + PEi + Wext = KEf + PEf**

What is an example using the equation?

A weightlifter applies an upwards force of 1000 N to a barbell to displace it upwards a given distance of 0.25 meters at a constant speed and begins with 1500 J of energy, find mechanical energy. W = 000 N•0.25 m•cosine 0 degrees = 250 J TMEi + Wext = TMEf 1500 + 250 = **1750 J**


 * C**

What is the work energy relationship?

Energy can be used to do work and work can be used to transfer energy. Work = the change in kinetic energy.

When is kinetic energy gained and lost?

A roller-coaster at the top of a hill is a common analogy used here. The roller-coaster has the potential to expend a lot of energy, but currently it is not. Kinetic energy is while it is going down the hill. Once it stops moving from the momentum gained, it will no longer have kinetic energy.

When is there maximum kinetic energy?

The maximum kinetic energy is present at the instance it strikes the ground

What is an example of the work energy relationship?

When a book sliding across the floor to rest; frictional forces do work on the book and change its kinetic energy.

=Electric Bill=



Monthly = $18.60


 * Calculations:**



The cost of electric does seem a lot to me since it is in larger end of the range $.10 - $.20. However, when looking at the cost for each appliance, the numbers seem really small and I did not expect these numbers to add up to such a large number. With all appliances added, my family's electric bill is $164.44 for one month which is a big difference compared to the cost of 10 appliances chosen, $18.60. Major appliances such as a refrigerator, all the lighting, and our electric fireplace make a huge contribution to the amount that we pay for electric. Perhaps, my family should start to turn off the lighting more often which may be difficult because there's always someone staying up really late. In addition, we have 3 running refrigerators in my house, maybe we could try to clean one out and eliminate it.