Which statement best explains acceleration? a. it is the total distance covered over a period of time. b. it is a change in velocity over a period of time. c. it is a change in displacement over a period of time. d. it is a change in direction over a period of time.

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

Amira pulls a 3 pound wagon 4 feet. how much work has she done?

2. which of the following does not affect the electrical resistance of a body? a. material composing the body b. bodies directly surrounding the body c. length of the body > d. temperature of the body