Physics Homework: An Earthlike Planet?
In January 2006, astronomers reported the discovery of a planet comparable in size to the earth orbiting another star and having a mass of 5.50 times the earth's mass. It is believed to consist of a mixture of rock and ice, similar to Neptune. Take mEarth=5.97×1024kg and rEarth=6.38×106m. 1. If this planet has the same density as Neptune (1.76 g/cm3), what is its radius expressed in kilometers? 2. What is its radius expressed as a multiple of earth's radius?
If a time traveller were to kill a random human 20,000 years ago, what is the greatest hypothetical effect that it could have on our modern era?
That’s a great question, and not easy to answer. Odds are the effect would be nil, since 20,000 years is so long ago, that it’s unlikely that the killing (if it occurred before the individual had reproduced) could have eliminated any gene or genetic material crucial to an individual important in our history, like Einstein or Hitler.If the individual was killed after passing on her or his genes to the next generation, then it’s even less likely that the killing would have any discernible effect. If, for example, the person who was killed helped develop the alphabet, chances are it still would have been developed by other people sooner or later anyway (due to the well-known phenomenon of multiple independent invention, as in Edison, the Lumiere Bros, and Friezse-Greene all inventing motion photography at pretty much the same time, and not working together).Back to the genetic component: the only way such a killing could have a discernible effect on our history is it it eliminated a genetic composition crucial to the intelligence and emotional disposition of someone who later became famous in history.