Answer:
book resting on a shelf has no potential energy relative to the shelf since it has a height of zero meters relative to the shelf. However, if the book is elevated to some height above the shelf, then it has potential energy proportional to the height at which it resides above the shelf.
An object can have both kinetic and potential energy at the same time. For example, an object which is falling, but has not yet reached the ground has kinetic energy because it is moving downwards, and potential energy because it is able to move downwards even further than it already has. The sum of an object's potential and kinetic energies is called the object's mechanical energy.
As an object falls its potential energy decreases, while its kinetic energy increases. The decrease in potential energy is exactly equal to the increase in kinetic energy.
Another important concept is work.
If the mass of one object is doubled, the force between these objects will also double.
Force refers to an influence on a body which can change its state of rest or motion.
Force F = G(mM/d^2) (where m is the mass of first object, M is the mass of the second object and G is the gravitational pull and d is the distance between the two objects)
The force between two objects (m and M) (according to the universal law of gravitation) is proportional to their mass and reciprocally proportional to the square of their separation (R) between them.
So F' = G(2mM/d^2),
which means F'=2F
Therefore, the when the mass is doubled, the force also doubles.
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<span> If a force is applied over a smaller surface area you get a larger <span>pressure</span></span>
The earth has had liquid water for 4billion years
Explanation:
The coordinates of points are:
A (0, 70, 0),
B (40, 0, 0), C (40, 0, 40) D (60, 0, 60).
The position vectors for corresponding cables are:
the unit vectors for these positions are:
![u_{AD} =r_{AD} /[r_{AD} ]=(-60/110)i-(70/110)j-(60/110)k\\=-0.5455i-0.6364j-0.5455k](https://tex.z-dn.net/?f=u_%7BAD%7D%20%3Dr_%7BAD%7D%20%2F%5Br_%7BAD%7D%20%5D%3D%28-60%2F110%29i-%2870%2F110%29j-%2860%2F110%29k%5C%5C%3D-0.5455i-0.6364j-0.5455k)
![u_{AC} =r_{AC} /[r_{AC} ]=-(40/90)i-(70/90)j+(40/90)k\\=-0.444i-0.778j+0.444k](https://tex.z-dn.net/?f=u_%7BAC%7D%20%3Dr_%7BAC%7D%20%2F%5Br_%7BAC%7D%20%5D%3D-%2840%2F90%29i-%2870%2F90%29j%2B%2840%2F90%29k%5C%5C%3D-0.444i-0.778j%2B0.444k)
![u_{AB} =r_{AB}/[ r_{AB} ]=(40/80.6)j-(70/80.6)j+0k\\=0.4963i-0.8685j+0k](https://tex.z-dn.net/?f=u_%7BAB%7D%20%3Dr_%7BAB%7D%2F%5B%20r_%7BAB%7D%20%5D%3D%2840%2F80.6%29j-%2870%2F80.6%29j%2B0k%5C%5C%3D0.4963i-0.8685j%2B0k)
The factors are:
![F_{AB} =[F_{AB} ]u_{AB} =0.9926i-1.737j+0k\\\\F_{AC}= [F_{AC]} u_{AC} =-0.8888i-1.5556j+0.8888k](https://tex.z-dn.net/?f=F_%7BAB%7D%20%3D%5BF_%7BAB%7D%20%5Du_%7BAB%7D%20%3D0.9926i-1.737j%2B0k%5C%5C%5C%5CF_%7BAC%7D%3D%20%5BF_%7BAC%5D%7D%20u_%7BAC%7D%20%3D-0.8888i-1.5556j%2B0.8888k)
![F_{AD} =[F_{AD}] u_{AD} =-1.0910i-1.2728j-1.0910k](https://tex.z-dn.net/?f=F_%7BAD%7D%20%3D%5BF_%7BAD%7D%5D%20u_%7BAD%7D%20%3D-1.0910i-1.2728j-1.0910k)
so The resultant force exerted on tower by cables are:
![F_{R} =F_{AB}+ F_{AC}+ F_{AD} \\=-0.9875i-4.5648j-0.2020k\\magnitude=[F_{R} ]=4.674kN](https://tex.z-dn.net/?f=F_%7BR%7D%20%3DF_%7BAB%7D%2B%20F_%7BAC%7D%2B%20F_%7BAD%7D%20%5C%5C%3D-0.9875i-4.5648j-0.2020k%5C%5Cmagnitude%3D%5BF_%7BR%7D%20%5D%3D4.674kN)
