# 0.3 Gravity and mechanical energy  (Page 5/9)

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If the suitcase falls off the cupboard, it will lose its potential energy. Halfway down the cupboard, the suitcase will have lost half its potential energy and will have only $9,8\phantom{\rule{2pt}{0ex}}J$ left. At the bottom of the cupboard the suitcase will have lost all it's potential energy and it's potential energy will be equal to zero.

Objects have maximum potential energy at a maximum height and will lose their potential energy as they fall.

A brick with a mass of $1\phantom{\rule{2pt}{0ex}}\mathrm{kg}$ is lifted to the top of a $4\phantom{\rule{2pt}{0ex}}m$ high roof. It slips off the roof and falls to the ground. Calculate the potential energy of the brick at the top of the roof and on the ground once it has fallen.

• The mass of the brick is $m=1\phantom{\rule{2pt}{0ex}}\mathrm{kg}$
• The height lifted is $h=4\phantom{\rule{2pt}{0ex}}m$

All quantities are in SI units.

• We are asked to find the gain in potential energy of the brick as it is lifted onto the roof.
• We also need to calculate the potential energy once the brick is on the ground again.
1. Since the block is being lifted we are dealing with gravitational potential energy. To work out $PE$ , we need to know the mass of the object and the height lifted. As both of these are given, we just substitute them into the equation for $PE$ .

2. $\begin{array}{ccc}\hfill PE& =& mgh\hfill \\ & =& \left(1\right)\left(9,8\right)\left(4\right)\hfill \\ & =& 39,2\phantom{\rule{0.166667em}{0ex}}\mathrm{J}\hfill \end{array}$

## Gravitational potential energy

1. Describe the relationship between an object's gravitational potential energy and its:
1. mass and
2. height above a reference point.
2. A boy, of mass $30\phantom{\rule{2pt}{0ex}}\mathrm{kg}$ , climbs onto the roof of a garage. The roof is $2,5\phantom{\rule{2pt}{0ex}}m$ from the ground. He now jumps off the roof and lands on the ground.
1. How much potential energy has the boy gained by climbing on the roof?
2. The boy now jumps down. What is the potential energy of the boy when he is $1\phantom{\rule{2pt}{0ex}}m$ from the ground?
3. What is the potential energy of the boy when he lands on the ground?
3. A hiker walks up a mountain, $800\phantom{\rule{2pt}{0ex}}m$ above sea level, to spend the night at the top in the first overnight hut. The second day he walks to the second overnight hut, $500\phantom{\rule{2pt}{0ex}}m$ above sea level. The third day he returns to his starting point, $200\phantom{\rule{2pt}{0ex}}m$ above sea level.
1. What is the potential energy of the hiker at the first hut (relative to sea level)?
2. How much potential energy has the hiker lost during the second day?
3. How much potential energy did the hiker have when he started his journey (relative to sea level)?
4. How much potential energy did the hiker have at the end of his journey?

## Kinetic energy

Kinetic Energy

Kinetic energy is the energy an object has due to its motion.

Kinetic energy is the energy an object has because of its motion. This means that any moving object has kinetic energy. The faster it moves, the more kinetic energy it has. Kinetic energy ( $KE$ ) is therefore dependent on the velocity of the object. The mass of the object also plays a role. A truck of $2 000\phantom{\rule{2pt}{0ex}}\mathrm{kg}$ , moving at $100\phantom{\rule{2pt}{0ex}}\mathrm{km}·\mathrm{hr}{}^{-1}$ , will have more kinetic energy than a car of $500\phantom{\rule{2pt}{0ex}}\mathrm{kg}$ , also moving at $100\phantom{\rule{2pt}{0ex}}\mathrm{km}·\mathrm{hr}{}^{-1}$ . Kinetic energy is defined as:

Is there any normative that regulates the use of silver nanoparticles?
what king of growth are you checking .?
Renato
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
why we need to study biomolecules, molecular biology in nanotechnology?
?
Kyle
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
why?
what school?
Kyle
biomolecules are e building blocks of every organics and inorganic materials.
Joe
anyone know any internet site where one can find nanotechnology papers?
research.net
kanaga
sciencedirect big data base
Ernesto
Introduction about quantum dots in nanotechnology
what does nano mean?
nano basically means 10^(-9). nanometer is a unit to measure length.
Bharti
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
absolutely yes
Daniel
how to know photocatalytic properties of tio2 nanoparticles...what to do now
it is a goid question and i want to know the answer as well
Maciej
Abigail
for teaching engĺish at school how nano technology help us
Anassong
Do somebody tell me a best nano engineering book for beginners?
there is no specific books for beginners but there is book called principle of nanotechnology
NANO
what is fullerene does it is used to make bukky balls
are you nano engineer ?
s.
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
Tarell
what is the actual application of fullerenes nowadays?
Damian
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
Tarell
what is the Synthesis, properties,and applications of carbon nano chemistry
Mostly, they use nano carbon for electronics and for materials to be strengthened.
Virgil
is Bucky paper clear?
CYNTHIA
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
NANO
so some one know about replacing silicon atom with phosphorous in semiconductors device?
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
Harper
Do you know which machine is used to that process?
s.
how to fabricate graphene ink ?
for screen printed electrodes ?
SUYASH
What is lattice structure?
of graphene you mean?
Ebrahim
or in general
Ebrahim
in general
s.
Graphene has a hexagonal structure
tahir
On having this app for quite a bit time, Haven't realised there's a chat room in it.
Cied
what is biological synthesis of nanoparticles
how did you get the value of 2000N.What calculations are needed to arrive at it
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