S defined by the International Astronomical Union<span> (IAU), a light-year is the distance that </span>light travels in vacuum<span> in one </span>Julian year<span> (365.25 days). so if a planet </span><span>15 light-years away from Earth that is inhabitable by humans like us they have developed a very powerful telescope allowing them see what is happening on Earth if they look to the telescope today, they will see 15 years ago in the earth</span>
Answer:
Explanation:
In 1789, Antoine Lavoisier published a list of 33 chemical elements. Although Lavoisier grouped the elements into gases, metals, non-metals, and earths, chemists spent the following century searching for a more precise classification scheme. In 1829, Johann Wolfgang Döbereiner observed that many of the elements could be grouped into triads (groups of three) based on their chemical properties. Lithium, sodium, and potassium, for example, were grouped together as being soft, reactive metals. Döbereiner also observed that, when arranged by atomic weight, the second member of each triad was roughly the average of the first and the third.[19] This became known as the Law of Triads.[20] German chemist Leopold Gmelin worked with this system, and by 1843 he had identified ten triads, three groups of four, and one group of five. Jean Baptiste Dumas published work in 1857 describing relationships between various groups of metals. Although various chemists were able to identify relationships between small groups of elements, they had yet to build one scheme that encompassed them all.[19]
Answer:
Explanation:
The electric potential energy is the potential energy that results from the Coulomb force and is associated with the configuration of two or more charges. For an electron in the presence of an electric field produced by a proton, the electric potential energy is defined as:
where 
is the electron charge, 
is the proton charge, r is the separation distance between the charges and k is the coulomb constant.
Knowing this, we can calculate how much electric potential energy was lost:
Picking up a box, pushing a box along the ground, and pulling a box along the ground (B, C, and D) definitely involve work being done.
If a person CARRIES a box from one place to another, AND keeps it at the same height during the entire carry, then no work is done. ( A )
Answer:
Hey how are you today
Your answer would be B sound and ocean waves.
The reason why of course is because mechanical waves are waves that travel through matter and not empty space (as for light travels through empty space and is therefore not a machanical wave). and x-rays are a spectrum of light so they aren't mechanical waves eather.
Hope it helped
