Select all the correct answers. Which two statements are true about a system?

- A system is a group of objects analyzed as one unit.
- Energy that moves across system boundaries is conserved. - There's only one way to define the boundaries of a system.
- All systems are made by humans.​

What is meant by the statement" the melting poin of glycerine is 13 degree celsius

Glass is transparent to visibile light under normal conditions; however, at extremely high intensities, glass will absorb most of the light incident upon it. this works through a process known as multiphoton absorption. in this process, several photons are absorbed at the same time. if very intense light whose photons carry 2ev of energy is shined onto a material with a band gap of 4ev, that light can be absorbed through two-photon absorption, because two photons have the right amount of energy to bridge the band gap. what is the minimum number of photons of 800-nm light that are needed to equal or exceed the band gap of fused silica glass

If vx = 7.00 units and vy = -7.60 units, determine the magnitude of v⃗ . determine the direction of v⃗ .