Alex is asked to move two boxes of books in contact with each other resting on a rough floor. he decides to move both of them at the same time by pushing on box a with a horizontal pushing force of fp=8.9 n. here a has a mass of ma= 11.0 kg and b has a mass of mb= 7.0 kg. the contact force between the two boxes is fc. the coefficient of kinetic friction between the boxes and floor is .02. (assume fp acts in the +x direction)a) what is the magnitude of the acceleration of the two boxes? m/s^2b) what is the force exerted on mb by ma. in other words what is the magnitude of the contact force fc? nc) if alex were to push from the other side on the 7.0 kg box, what would the new magnitude of fc be?

An object is located 30.0 cm from a concave mirror. the focal length is 15.0 c,. what is the image distance? a. 30.0 cm b. -10 cm c. 10.0 cm d. -30.0 cm

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

Which of the following are guidelines to follow for obtaining accurate observations