PEMERINTAH KOTA PADANG
DINAS PENDIDIKAN
SEKOLAH MENENGAH ATAS(SMA) NEGERI 10 PADANG.
Situjuh Telp (0751)27331 Padang Kode Pos 25129
LESSON PLAN
WORK AND ENERGY
A. Identities
| Subject | : Physics |
| Class/semester | : XI / I |
| Meeting to | : 3, 4 |
| Time Allocation | : 2 x 45 minutes |
| Standard competency | : Analyze physics phenomena and it’s regularly in scope mechanics particle object |
| Base competency | : Analyze relationship between work, energy change and the Law of Conservation of Mechanical Energy |
| Indicators | : Describe relationship among work, force, displacement
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A. Learning objectives : - The students are able to :
1. Observe requirement of work
2. Calculate the work done by force on smooth plane through experiment
3. Calculate the work done by force on incline plane through experiment
4. Calculate the work by several forces
5. Calculate the work from F-x graph
B. Learning materials : 1. Work is product of force with displacement which is in the same direction
The work W done on an object by an agent exerting a constant force on the object is the product of the component of the force in the direction of the displacement and the magnitude of the displacement:
2. Factors influence the magnitute of work
3. Formulation of work is:
W = F cos θ.∆x
4. Work by several forces :
W = W1 + W2 + W3 +……….
KINETIC ENERGY AND THE WORK – KINETIC ENERGY THEOREM
Figure shows a particle of mass m moving to the right under the action of a constant net force ∑F. Because the force is constant, we know from Newton’s second law that the particle moves with a constant acceleration a. If the particle is displaced a distance d, the net work done by the total force ∑F is
We found that the following relationships are valid when a particle undergoes constant acceleration:
where vi is the speed at t _ 0 and vf is the speed at time t. Substituting these expressions into Equation gives
The quantity represents the energy associated with the motion of the This quantity is so important that it has been given a special name kinetic energy. The net work done on a particle by a constant net force F acting on it equals the change in kinetic energy of the particle. In general, the kinetic energy K of a particle of mass m moving with a speed v is defined as
Kinetic energy is a scalar quantity and has the same units as work.
in the form
C. Learning methods: experiment, discussion, task
D. Stages of learning activities
| No | Learning activities | Time allocation | Sources/Material /Tools |
| 1 | Opening activities Ø Teacher checks students attendance Ø students collect the previous task of report Ø Apperception: § Is it the same the definition of work in physics with the term of work known in daily life? Ø Motivation : § Is lifter that lift the told do the work? If that lifter hold back the load on it, does it belong doing the work? Ø Teacher delivers base competency about : § Analyze relationship between work, energy change and the Law of Conservation of Mechanical Energy analysis.
Main Activity Exploration · The students sit in group · Teacher give LKS
Elabiration · Student do experiment that is suitable with guidance in LKS and discuss the result in group. The teacher goes around to control and be ready to help the students if needed
· From the data got the students do analyzing so that can write the conclusion by making pratical report · The students mention application samples of work concept of daily life
Confirmation · Teacher give some concept applications in determine resultant of work an energy of object in daily life. · Teacher gives examples of physics problem to determine the work and energy . The students look and write example of physics problem and it’s solution that given by teacher. Closing Activities · Teacher checks concept mastery of students and make the conclusion together. · Teacher gives award to group that has good work and relationship. · Teacher gives homework to student and task student to read material that will be studied in the next meeting | 10’
10’
5’ 5’
40’
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5’
5’
5’
5’
| Sources : a. physics book of class XI semester 1 b. Relevance of reference book c. Work sheet (LKS) d. Tools and material of experiment
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E. Assesment.
a. Observation format
b. Performance
1. Consider a tug-of-war in which two teams pulling on a rope are evenly matched so that no motion takes place. Assume that the rope does not stretch. Is work done on the rope? On the pullers? On the ground? Is work done on anything?
2. For what values of _ is the scalar product (a) positive and b) negative?
3. As the load on a spring hung vertically is increased, one would not expect the Fs-versus-x curve to always remain linear, as shown in Figure 7.10d. Explain qualitatively, what you would expect for this curve as m is increased.
4. Can the kinetic energy of an object be negative? Explain.
5. (a) If the speed of a particle is doubled, what happens its kinetic energy? (b) If the net work done on a particle is zero, what can be said about the speed?
6. A tugboat exerts a constant force of 5 000 N on a ship moving at constant speed through a harbor. How much work does the tugboat do on the ship in a distance of 3.00 km?
7. A shopper in a supermarket pushes a cart with a force of 35.0 N directed at an angle of 25.0° downward from the horizontal. Find the work done by the shopper as she moves down an aisle 50.0 m in length.
8. A raindrop (m _ 3.35 10_5 kg) falls vertically at constant speed under the influence of gravity and air resistance. After the drop has fallen 100 m, what is the work done (a) by gravity and (b) by air resistance?
9. A sledge loaded with bricks has a total mass of 18.0 kg and is pulled at constant speed by a rope. The rope is inclined at 20.0° above the horizontal, and the sledge moves a distance of 20.0 m on a horizontal surface. The coefficient of kinetic friction between the sledge and the surface is 0.500. (a) What is the tension of the rope? (b) How much work is done on the sledge by the rope? (c) What is the energy lost due to friction?
10. A block of mass 2.50 kg is pushed 2.20 m along a frictionless horizontal table by a constant 16.0-N force directe 25.0° below the horizontal. Determine the work done by (a) the applied force, (b) the normal force exerted by the table, and (c) the force of gravity. (d) Determine the total work done on the block.
11. A 15.0-kg block is dragged over a rough, horizontal surface by a 70.0-N force acting at 20.0° above the horizontal. The block is displaced 5.00 m, and the coefficient of kinetic friction is 0.30
12. Find the work done by (a) the 70-N force, (b) the normal force, and (c) the force of gravity. (d) What is the energy loss due to friction? (e) Find the total change in the block’s kinetic energy
13. A person lifts an object of mass 1,5 kg vertically upward through a distance of 2.0 m with constant speed. Determine (a) the work done by the person, (b) the work done by the gravitational force,(c) the total work by the two force.
14. An object of mass 1.5 kg slides downwards on a smooth Inclined plane AC of length 25.0 m. Determine the work Done by the gravitational force in order to displace the Object from A to B.
KNOW BY PADANG, 25 JUNI 2010
PRINCIPLE R VICE PRINCIPLE PHYSICS TEACHER
DRS.Safarni Budaya Putra Haryanti,M.Pd Desmalinda, S.Pd,
NIP : 19501122 197903 1005 NIP : 196807171995122002 NIP : 19671205 199702 2 001
