Energycapacity to do WORK
F x DD = distance moved in the direction of force applied
1 Joule = 1 Newton meter1 J = 1 Nm
Quiz Which of the following are forms of
energy?
a. Soundb. Nuclearc. Elastic Potentiald. Chemical Potentiale. Jolues
Quiz In which of the following cases is work
done?
A. A person pushing a wooden box forward.
B. A person pushing the wall of a building.
C. An athlete trying to compress a shot put.
D. Two opposing teams of people pulling a tug-of-war rope which is stationary.
F x DWORK =
Quiz An object of mass 20 kg is pulled up a slope of 15m long as shown in Figure. The frictional force between the object and the slope is 30 N. a)What is the work done by the frictional force?b)What is the total work done in pulling the object up the slope?
20kg5 m
15 m
Gravitational Potential Energy
Energy a body has due to its position.
Ep = mgh
Ep = GPE (J)m = mass (kg)g = gravitational field strength (N/m)h = height (m)
Conservation of Energy
Energy can neither be created nor destroyed in any process.
It can be converted from one form to another or transferred from one body to another, but the total amount remains constant.
Conservation of Energy
KE = 0
PE = max
Assume negligible air resistance
KE = 0
PE = max
KE = max
PE = 0
Conservation of Energy
If air resistanceis NOT negligible
http://www.youtube.com/watch?v=CgqBg44azYk
Youtube video
45 45 - 49 12
Quiz Conversion of energy
Which one of the following correctly describes the energy conversion that occurs after a bungee jumper jumps from the bridge to the instant when the chord is extended to the maximum?
A. EPE KE GPEB. GPE KE EPEC. GPE EPE KED. KE GPE EPE
EPE = elastic potential energy
KE = kinetic energy
GPE = gravitational potential energy
RecapGive examples of the various form of energy
state the principle of the conservation of energy
Give the formula for calculating KE and GPE?
apply the relationships for KE and GPE to new situations or to solve related problems
recall and apply the relationship work done = force x distance moved in the direction of the force to new situations or to solve related problems
QuizConservation of EnergyAn acrobat of mass 70 kg jumps down on to the seesaw and lift his partner upward. (Assume negligible air resistance and frictions Take g=10 N kg-1)(i) Calculate the loss of gravitational potential energy when the acrobat touches the see saw.(ii) What is the speed of the acrobat just before touching the see saw? (iii) Given that his partner has a mass of 60 kg, how high would he reach?
3 m
QuizWork done
A bullet of mass 50g was travelling at a speed of 200ms-1 before striking a sandbag. It travelled through 20cm of the sandbag before stopping.
What was the total resistive force
produced by the sandbag?
QuizA windmill is used to raise water from a well. The depth of the well is 5 m. The windmill raises 200 kg of water every day. What is the useful power extracted from the wind?