Câu 1: Một chiếc xe chạy trên đoạn đường 40km với tốc độ trung bình là 80km/h, trên đoạn đường 40km tiết theo với tốc độ trung bình là 40km/h. Tốc độ trung bình của xe trên đoạn đường 80km này là.?? Câu 2: Một chiếc xe từ A đến B mất một khoảng thời gian t với vận tốc trung bình là 48km/h. Trong 1/4 khoảng thời gian đầu nó chạy với vận tốc trung bình 30km/h. Trong khoảng thời gian còn lại nó với vận tốc trung bình bằng??

Curious carl calculated the density of a cube to be 4.50 g/cm3. what is the density of the cube in g/l?

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

Suppose that two tanks, 1 and 2, each with a large opening at the top, contain different liquids. a small hole is made in the side of each tank at the same depth 1.57 m below the liquid surface, but the hole in tank 2 has 2.49 times the cross-sectional area of the hole in tank 1. (a) what is the ratio ρ1/ρ2 of the densities of the liquids if the mass flow rate is the same for the two holes? (b) what is the ratio rv1/rv2 of the volume flow rates from the two tanks? (c) at one instant, the liquid in tank 1 is 14.9 cm above the hole. if the tanks are to have equal volume flow rates, what height above the hole must the liquid in tank 2 be just then?