# 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:

Leo Robinson's definition
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what is quantity2
An indefinite amount of something.
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in ordinary sense demand means desire
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demand in economics means both willingness as well as the ability to purchase a commodity by paying a price an also its actuall purchase
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demand refers to the various quantity of goods and services that consumers are willing and able to purchase at a particular period of time all other things been equal
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The amount of a good or service that consumers are willing to buy at a particular price.
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what is cost pull inflation?
oru
demand is economic principle referring to a consumer's desire and willingness to pay a price for a specific or service..
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utility is the among of certisfaction driving from using a comundity
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mention and explain two Bank I financial institutions and two non baking financial institutions
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Demand-pull inflation is asserted to arise when aggregate demandin an economy outpaces aggregate supply. It involvesinflation rising as real gross domestic product rises and unemployment falls, as the economy moves along the Phillips curve.
kevin
Perfectly elastic demand
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demand of any good demanded more after a certain period. if a commodity prices may high and scarcity of that resources.
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cannot demand more
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cross elasticity of demand is an economic concept that measures the responsiveness in the quantity demand of one good when a change in price takes place in other good
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this is responsiveness quantity demanded keeping other factors constant
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CONDITIONS OF PERFECT MARKET: 1. Perfect competition(PC): no increasing returns, many buyers and sellers, all are price takers, not prices makers. 2. Perfect Information (PI): buyers and sellers know all they need to know about what they are buying and selling to make the right decisions.
Mallekha
3. Complete Markets(CM): no externalities or public goods, no transactions costs, "thick" markets.
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nice contributor
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A numerous downsized market that does not meet standards.
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A Perfect Market is a numerous downsized market that does not meet standards.
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is place where buyers and sellers met together for the purpose of buying and selling of good and services
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after 100 year this will be not nanotechnology maybe this technology name will be change . maybe aftet 100 year . we work on electron lable practically about its properties and behaviour by the different instruments
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name doesn't matter , whatever it will be change... I'm taking about effect on circumstances of the microscopic world
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At high concentrations (>0.01 M), the relation between absorptivity coefficient and absorbance is no longer linear. This is due to the electrostatic interactions between the quantum dots in close proximity. If the concentration of the solution is high, another effect that is seen is the scattering of light from the large number of quantum dots. This assumption only works at low concentrations of the analyte. Presence of stray light.
the Beer law works very well for dilute solutions but fails for very high concentrations. why?
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