The meter was redefined as a reference to earth, then to krypton, and finally to the speed of light. why do you think the reference point for a meter continued to change?

Comedians like to joke that the reason we haven’t been visited by intelligent life from elsewhere in the universe is that aliens have been monitoring earth’s broadcasts of intellectually embarrassing tv programs, like gilligan’s island, fear factor, the jersey shore, and the jerry springer showand so consider us far too primitive to merit a visit. let’s check the assertion that aliens could have been receiving them. tv programs are broadcast at a frequency of about 100mhz with about 100kw of total power in 30frames per second, which emanatesroughly uniformly in all directions. assume that interstellar space transmits these broadcasts without attenuation. no matter how smart they are, aliens would require at least one photon per frame to interpret our signals. findthe number of photons per unit time per unit area reaching a receiver on a possible planet in the nearest star system, which is about 4 light-years away (a light-year is the distance light travels in a year). if aliens aimed a receiver or detector directly at earth, how big (in diameter) would it have to be to receive a photon per frame

Aforce of 100 newtons is used to move an object a distance of 15 meters with a power of 50 watts. find the work dine and the time it takes to do the work

This chart shows characteristics of three different types of waves. which statement is best supported by the information in the chart? wave x and wave y are mechanical waves, and wave z is an electromagnetic wave. wave x and wave y are electromagnetic waves, and wave z is a mechanical wave. wave x and wave z are electromagnetic waves, and wave y is a mechanical wave. wave x and wave z are mechanical waves, and wave y is an electromagnetic wave.