Practicing Physics (Work)

Classjump.com/s/sidiq
http://www.classjump.com/s/sidiq/documents/Worksheet31Work.pdf?
------------------------------------------------------------------------------------------------------------------
Classjump worksheet 
Doing the even numbers
Process of solving / Examples


2. A tugboat pulls a ship with a constant force of 5000 N, causing the ship to move through a harbor. How much work does the tugboat do on the ship if each moves a distance of 3 km?

W=5000Nx3000m
=15000000 Joules
=15Mega Joules

4. A husky dog does 20 kJ of work as he pulls a sleigh with a force of 340 N. Through what distance does he pull it?
W/F=S
20000J/340N = S
                       = 58.8m

6. What is the weight of a mass of 100 kg? Find the work done in raising a mass of 100 kg through a vertical height of 60 m.

1000N x 60m = 60000Joules
                       = 60KJ

8. Carlos does a chin-up in gym class and raises himself 0.8 m.  If Carlos has a mass of 62 kg, how much work does he accomplish? 

W= 620Nx0.8 =490 Joules

10. A girl pushes her little brother on his sled with a force of 300 N for 750. m.  How much
work is this if the force of friction acting on the sled is
(a) 200 N?
(b) 300 N?

(a) W= (300-200) x 750 = 75000 Joules
(b) W= (300-300) x 750 = 0 Joules

Energy

Science for Junior High School

2nd Semester Grade VIII

----------------------------------------------------------------------------------------------------------------------------------

Science Text Book Page 52-57

What is Energy

What are the forms of energy in terms of physics

A. What is Energy

                Energy is a "power" that makes the work occur. Which means it is the capacity of a physical system to work. It has many types of energies, those are chemical energy, thermal energy, sound energy, light energy, electrical energy, nuclear energy, and the most important mechanical energy. Since work and energy have a relation, energy is also Joules (J) like work. 

B. Forms of Energy

DEFINITION

EXAMPLES

                  As is explained above, there are many types of energy. Those are chemical energy, thermal energy, sound energy, light energy, electrical energy, nuclear energy, and mechanical energy. In this section B, I will going to explain each types of the energy, and also the definition of it.

1. Chemical Energy: Chemical energy is the energy mostly contained in your body. You can also find chemical energy in food, and some natural resources such as coal, oil, and natural gas. Joules (energy) that are produced by food is kept in the human body in order to perform activities. Most dominant energy resource of food is carbohydrates (rice, bread, grains) and also fat (Milk, butter, oil).

2. Thermal energy: Thermal energy is the energy related with the really small motion of particles producing a heat. You can find thermal energy by rubbing hands together, and also from everywhere that produces heat. Such as, a geyser. 

3. Sound energy: Sound energy is the energy produced through the vibration of air particles around a sound source.  Think of a car horn for an example. It produces vibration on air particles because of a strong sound

4. Light energy: Light energy is the energy produced by the radiation of electromagnetic waves. For an example, Earth gets brighten up because of the sun illuminating the darkness of the space near an Earth.

5. Electrical energy: Electrical energy is the energy produced by electrical charges which move through the cables. For example, a laptop is being charged by the charger which uses the electrical energy. 

6. Nuclear energy: Nuclear energy is the energy released from the reaction of the nucleus of radioactive matters. There are two kinds of nuclear energy; they are a fusion energy ( the join of the nucleus of an atom) and a fission energy (the split of the nucleus of an atom). Power plant is a great example of nuclear energy.The most visible source of nuclear energy are the more than 400 worldwide power plants that function on nuclear reactors. These reactors contain the reaction of nuclear fission, which produces heat that is then used to create electricity. More than 20 percent of power in the United States is produced by these power plants.

7. Mechanical energy: Mechanical energy is the energy associated with motion. Which means is an energy of an object due to its motion or position. Mechanical energy can be either kinetic energy (energy of motion) or potential energy (stored energy of position). A moving car possesses mechanical energy due to its motion (kinetic energy).A moving baseball possesses mechanical energy due to both its high speed (kinetic energy) and its vertical position above the ground (gravitational potential energy). A World Civilization book at rest on the top shelf of a locker possesses mechanical energy due to its vertical position above the ground (gravitational potential energy). A barbell lifted high above a weightlifter's head possesses mechanical energy due to its vertical position above the ground (gravitational potential energy). A drawn bow possesses mechanical energy due to its stretched position (elastic potential energy).

Science Text Book 44-45 / Formula of Work

Science for Junior High School

2nd Semester Grade VIII

----------------------------------------------------------------------------------------------------------------------------------

Science Text Book Page 44-45 

Formula of Work in terms of Physics

A. Work

*Highlighted parts = Important 

In terms of physics, work means a force that causes an object move. However, if a force doesn't make an object move, it isn't considered as work.

1. What is work?

         Work is a force that causes an object move as explained above. To be stated as work in terms of physics, it has several requirements. Firstly, it needs a force that causes displacement of the object. Additionally  the direction of the force has to be the same as the direction of the displacement. 

         Examples of Work in sports : 

Dwight Howard superman dunk

Basketball players produces force to lift the ball up high. Since the ball is moved from player's hand to the higher part, basketball player is considered as doing a work.

Weight lifting world champion Lu Xiaojun

Athlete of weight lifting is probably the job that requires the most work. Lu Xiaojun who is world record holder for weight lifting has great muscles to provide the work. When an athlete is lifting a weight from the floor and holds it above his head, he is considered as doing work. However, if an athlete is holding up the weight and stay still (with no displacement) in physics it is considered as not doing work. Although the athlete is producing muscular force, the weight is still being kept in her hands and not moving anywhere. 

We can conclude that If a force doesn't cause any displacement, then the work is zero. If a force doesn't have the same direction as the displacement, then the work is also zero. 

This is another example of a force that doesn't have the same direction as the displacement so the work is zero.

Waiters holding up the tray is a good example for the force that doesn't have any work. Waiter is giving a force upwards to the tray while moving. So the tray is moving the right side as the white arrow represent, and the waiter is giving a force upwards as the black arrow represent. The tray is having a displacement without giving an external force on it. We could conclude that work is zero in this example.

2. Formula of Work 

The work done by a constant force of magnitude F on a point that moves a distance d in the direction of the force is the product. 

W= F x s

Work = Force x Displacement

If there are two forces act on one object, the force should be decreased or added. 

-Units-

F = Force, unit of measurement is N (Newtons)

s = Displacement, unit of measurement is m (Meters)

W = Work, unit of measurement is J (Joules)

Example of finding a Work in proper way

1. What is the work needed to push a box with a 100 N force, so that the box moves for 276m?

Solution: 

Force F= 100N

Displacement s = 276m

W = Fs

    = 100N x 276m = 27600 Joules

Tug of war is also a great example for how several forces act. If left side produces 150N of force and opposite side produces 100N. 

Solution of finding the greater force:

Force F= <-150N-100N->

Left side has greater force, so conclusively its <-50N by decreasing each other 150N-100N = 50N