China’s 1st large-scale sodium battery energy storage station put into operation
Category Archives: 07 Energy Work and Power
Possible for Singapore to have renewable geothermal energy from Sembawang hotspring?
Ratio of KE to GPE at 10m
Trash bag – energy transfer and inertia
How to mark 2 points (at a distance apart) at the same level? (water finds its own level)
The video below demonstrates that water will find its own level.
An olevel question requires this concept:
An apartment block receives water from a nearby reservoir. A pump is necessary to lift the water into a storage tank at the top of the building.
The gravitational field strength is 10 N / kg. How much energy does the pump supply to lift each kilogram of water into the tank?
Solutions: 100J
Water will always find its own level. Hence with or without the pump, the water level in the pipe in the building will be of the same level as the reservoir. Hence, the pump is only needed to pump water up a height of 10m only (instead of the 50m).
Energy, E = mgh = 1 kg x 10 N/kg x 10m = 100 J
Oscillating or Vibrating Object in a Wave Motion
When an object is oscillating or vibrating in a wave motion, the speed of the object varies along the path.
In this video, there are 3 examples of vibrating object.
1) Mass vibrating vertically from a spring
2) Pendulum bob oscillating
3) A particle vibrating up and down on a transverse wave
In general, when the object is at the extreme ends of the oscillation or vibration, it is momentarily at rest. Hence its KE at these points is minimum or 0 J.
And in the middle that is where the object is travelling the fastest, hence the KE is the maximum.
Understanding Conservation of Energy and applying in calculation questions
Tidal wave energy
Conservation of energy on the complete driver golf swing
Slinky Coil – Interesting Tricks and demonstrations of Transverse and Longitudinal Waves
Slink coil is usually used to demonstrate the two types of waves – transverse and longitudinal waves. But remember that when you are asked to state an example of each wave, do not quote slinky coil.
View the videos below to know more about the two types of waves.
Fiery Re-entry into Earth’s Atmosphere
SpaceX’s Crew Dragon heat shield shown off after first orbital-velocity reentry
How do spacecraft re-enter the Earth? | HowStuffWorks
Why Is It So Difficult For A Returning Spacecraft To Re-Enter Our Atmosphere?
Returning from Space: Re-entry – PDF format
SpaceX In-Flight Abort Test
SpaceX Falcon Heavy- Elon Musk’s Engineering Masterpiece
Shuttle Atlantis STS-132 – Amazing Shuttle Launch Experience
How to Land the Space Shuttle… from Space
Amazing wind walker beast
It’s amazing to watch these strandbeasts walk and solely powered by wind.
Wind energy to mechanical energy 🙂
This is a toy version of the wind walker.
This Huge Electric Dump Truck Never Needs to Plug In | WIRED
Transparent Solar Panels Will Turn Windows Into Green Energy Collectors
Force required to pull the block up the inclined plane
There are 3 scenarios with slight variations.
Calculate the force F needed to pull the block up the inclined plane.
View the video below to understand how to solve these types of question.
You can also view the solutions below.
Click here to view another post related to this concept: work done to bring an object up
A New “Solar Paint” Lets You Transform Your Entire House Into a Source of Clean Energy
Watch “CeramicSpeed DrivEN 99% Efficient Drive Shaft // Chain Free Bike // Eurobike 2018” on YouTube
Work done to bring an object up
Tesla powers a whole island with solar to show off its energy chops – The Verge
How wonderful it is if Singapore can be powered by the sun.
http://www.theverge.com/2016/11/22/13712750/tesla-microgrid-tau-samoa
Gravity Light – Amazing!
A perfect combination of Conservation of Energy and Magnetism!
Watch “Giant Xylophone in Forest – Beautiful Japanese TV Advert Commercial NTT Docomo” on YouTube
Every time I see this video, it never cease to impress me.
Conservation of Energy – Swinging Bowling Ball
Click here to view a lecture on COE by Walter Lewin. This comic is inspired by his demo at approx 48 mins of the video.
Why the truck has that bulky ugly thingy at the back?
The bulk thing at the back of these trucks is lowered down whenever these trucks have to stop along the road side for any forms of servicing, e.g. Repairing roads, digging to lay pipes etc.
It acts as a cushion just in case any vehicle on the road fail to notice the stationary truck and collide head on. With this cushion, the impact force on the car and hence on the driver will be greatly reduced.
Let us do a simple calculation. Assuming the incoming vehicle of mass 1000 kg traveling at 80 km/h (22.2m/s).
KE of vehicle = 1/2mv2 = 1/2 x 1000 x 22.2 x 22.2 = 246 420 J
All these energy of the vehicle will be converted to work done in stopping the vehicle as it collides with the truck.
1) If without the cushion, the stopping distance will be very little and the vehicle will come to a stop almost instantly. Let assume 0.2 m.
KE = WD
246 420 = F x 0.2
impact force, F = 1 232 100 N
2) With the cushion, the stopping distance can be increased. Assume 2.0 m, the average impact force is
KE = WD
246 420 = F x 2.0
Impact force, F = 123 210 N
Hence with the cushion, the vehicle will experience significant smaller impact force and it might save the driver.
Solar Charger
One of the best portable solar charger in the market. Joos Orange – just arrived from US.
Energy Question with Work Done against Friction
Solutions: Option A
N2007P1Q9 Pure Physics – Energy needed to pump water up a building
An apartment block receives water from a nearby reservoir. A pump is necessary to lift the water into a storage tank at the top of the building.
The gravitational field strength is 10 N / kg. How much energy does the pump supply to lift each kilogram of water into the tank?
Solutions: 100J
Water will always find its own level. Hence with or without the pump, the water level in the pipe in the building will be of the same level as the reservoir. Hence, the pump is only needed to pump water up a height of 10m only (instead of the 50m).
Energy, E = mgh = 1 kg x 10 N/kg x 10m = 100 J
My daughter is learning Physics =)
A good example of Conservation of Energy =)
Evan: Chemical Energy to Electrical energy to Gravitational Potential Energy to Kinetic Energy
Levonne: *yawn* ….. I’m so sleepy…… zzzzzzzzzzzzzzzzzzzzz
Bullet embedded in wooden block
At a training exercise, a policeman fires a pistol. A bullet of mass 10.0 g leaves the pistol horizontally at a speed of 500 ms-1. The bullet strikes and gets embedded in a stationary piece of wood of mass 1.0 kg which was suspended. Immediately after impact, the wood with the embedded bullet moves at a horizontal speed of 5.0 ms-1 and swings upwards to a vertical height of h from its initial position before stopping momentarily.
a) What is the initial kinetic energy of the bullet when it leaves the pistol?
b)What is the final kinetic energy of the wood and embedded bullet immediately after impact?
c) By comparing (a) and (b), what is the loss in kinetic energy? Account for this loss.
d) Calculate the vertical height, h, stating any assumption made. Assume the gravitational field strength is 10 N kg-1.
Solutions:
a) 1250 J
b) 12.6 J
c) 1240 J. The loss in kinetic energy is converted to heat and sound energy when the bullet strikes the wood and is embedded.
d) 1.25 m
Work Done is the same for all 3 paths
Work done in bringing an object up to a height, h, is independent on the path. Hence path A, B and C all have the same work done as the vertical height is the same.
Work Done = Gain in GPE
= mgh
= weight x vertical height
Work Done = Force x Distance moved in the direction of the force
In Physics point of view, WORK DONE = FORCE x DISTANCE moved in the direction of the force.
Hence, there is only work done when a force acting on a object produces a distance moved in the direction of the force.
Honda – The Cog – conservation of energy, isn’t Physics amazing!!
Check out this video on YouTube:
Sent from my iPad
森の木琴 – Beauty of Conservation of Energy :)
GPE to KE + Sound 😉 Check out this video on YouTube:
Sent from my iPad
Energy calculation involving Work Done against friction
A box of mass 2 kg has an initial speed of 10 m/s at the foot of the ramp. Given that the friction along the ramp is 2 N, calculate the height h that it reaches when the speed of the box is 5 m/s. (g = 10 m/s2 )
Solutions:
For this question, the additional thing to note is the work done against friction. All the energy possesses by the box at bottom is KE. This KE will decrease and be converted to remaining KE at height h + gain in GPE + work done against friction.
To find the work done against friction, we need to find the distance moved by the box on the inclined ramp, d.
sin60 = h / d
d = h / sin60
Conservation of energy,
KE at bottom = KE at h + GPE at h + friction force
1/2mv2 = 1/2mv2 + mgh + F x d
(1/2 x 2 x 102) = (1/2 x 2 x 52) + (2 x 10 x h) + (2 x h/sin60)
h = 3.36 m
Ratio of KE and GPE at various positions
A ball in thrown vertically up. D is the highest point the ball reached. Find the ratio of KE at B to the PE at C.
Solutions: 1 : 1
To solve such question, you have to apply conservation of energy. In other words, total energy of ball at any positions (A, B, C and D) is the same (no air resistance etc). There is no way to find KE as no speed is given. So to find KE, you need to find it indirectly with the help of PE.
Understand the concept here as there can be many variations of question asked.
Conservation of Energy – demo
This is a typical demo to illustrate conservation of energy. It will definitely be safe to remain stationary (if you release the ball from rest) as some of the energy of the ball will be converted to other forms like work done against air resistance. Hence, it will never reach the same height it is released, so will not never touch you.
Of course, if you give the ball a push, you are giving additional energy to the ball. That additional energy enable the ball to reach a greater height, hence most likely it will hit your face =)
Work Done, Energy and Power are Scalar Quantities
Work Done, Kinetic Energy (KE), Gravitational Potential Energy (GPE) and Power are all SCALAR quantities.
Many have asked if Work Done is scalar or vector? Though from our textbook, Work Done = Force x distance in the direction of the force.
In other words, Work Done = Force x Displacement
We already know that Force is a vector. Weight being a force, is also a vector quantity. Displacement is distance in a specific direction, hence it is a vector quantity too. In tertiary education, you will learn in details that the product (multiplication) of two vectors will result in a scalar or dot product.
Since it is out of syllabus, it will be good to use other ways to help you to understand and recall.
Method 1 Remember vector x vector will end up a scalar. Similar to (-)x(-) = (+) Method 2 Consider moving a box up to a certain height, work done or gain in GPE is constant regardless of the path it takes (diagonal or vertical). Hence direction is not important, therefore GPE is a scalar.
When considering KE, since KE = 1/2mv2 , similar to Method 1, v2 is actually velocity x velocity. Hence it product of 2 vectors, resulting in KE being a scalar.
Power = Energy Conversion/ time or Work Done / time,
since energy, work done and time are scalar, Power is a scalar quantity.
Other important note: Power = Rate of work done = Rate of energy conversion.
Work Done, Energy and Power are Scalar Quantities
Work Done, Kinetic Energy (KE), Gravitational Potential Energy (GPE) and Power are all SCALAR quantities.
Many have asked if Work Done is scalar or vector? Though from our textbook, Work Done = Force x distance in the direction of the force.
In other words, Work Done = Force x Displacement
We already know that Force is a vector. Weight being a force, is also a vector quantity. Displacement is distance in a specific direction, hence it is a vector quantity too. In tertiary education, you will learn in details that the product (multiplication) of two vectors will result in a scalar or dot product.
Since it is out of syllabus, it will be good to use other ways to help you to understand and recall.
Method 1 Remember vector x vector will end up a scalar. Similar to (-)x(-) = (+) Method 2 Consider moving a box up to a certain height, work done or gain in GPE is constant regardless of the path it takes (diagonal or vertical). Hence direction is not important, therefore GPE is a scalar.
When considering KE, since KE = 1/2mv2 , similar to Method 1, v2 is actually velocity x velocity. Hence it product of 2 vectors, resulting in KE being a scalar.
Power = Energy Conversion/ time or Work Done / time,
since energy, work done and time are scalar, Power is a scalar quantity.
Other important note: Power = Rate of work done = Rate of energy conversion.
Work done – Man jumps from height 3 m, what is the force exerted by his legs?
A boy of mass 40 kg jumps from rest from a platform of height 3 m. He lands by bending his knees and stops his body in 0.5 s after landing. What is the force exerted by his legs?
Solutions: 620 N
To solve this question, you need to apply conservation of energy (COE) to find the kinetic energy (KE) that the boy possesses just before he reaches the ground.
After which, you can solve the question using (1) Conservation of energy or (2) Kinematics to solve.
Using COE to find the KE just before he reaches the ground.
Method 1: Using Conservation of Energy (COE)
Method 2: Using Kinematics
You must know these 2 methods and always think along this 2 directions when dealing with such questions.