Suppose an astronaut travels very fast from the Earth to the nearest star system, Alpha Centauri, located 4.30 light years (ly) away as measured by an Earth-bound observer. (a) How long does it take the astronaut to travel 4.30 ly at 0.99850 c (as measured by the Earth-bound observer)

Consider a file currently consisting of 200 blocks. assume that the file control block (and the index block in the case of indexed allocation) is already in memory. calculate how many disk i/o operations are required for contiguous, linked, and indexed (single-level) allocation strategies, for each of the conditions listed below. in the contiguous-allocation case, assume that there is not room to grow at the beginning but there is room to grow at the end. also assume that the block information to be added is stored in memory.

The radioactive isotope of lead, pb-209, decays at a rate proportional to the amount present at time t and has a half-life of 3.3 hours. if 1 gram of this isotope is present initially, how long will it take for 80% of the lead to decay? (round your answer to two decimal places.)

Definition: this is the weighted average of all of the isotopes of an element.