正确回答三道就可以给分
Question1.Howmanypeoplearetalkingontheircellphonesatthisinstant?
Question2.Howlargeamooncanyoujumpoffof?
Inotherwords,assumingreasonabledensities,whatistheradiusof
thelargestrockyspherefromwhichyoucanreachescapevelocity
byjumping?Estimateyouranswerwithinafactorof10.
Question3.Acceleration
Estimateandcomparetheaccelerationsofa)ajetairplanetaking
off,b)acaracceleratingtohighwayspeed,andc)apersonstarting
onawalk.
Question4.StoptheWorld,IWanttoGetoff
Ifeveryhumanranfor10secondsasfastaspossibletotheeast,
bywhatfractionwouldtheychangetheEarth’sangularvelocity
arounditsaxis(whiletheywererunning)?
Question5.Automobilekineticenergy
Comparethekineticenergyofacardrivingonthehighwaywith
thechemicalenergyrequiredtokeepdrivingforoneminuteandfor
onehour.Whatfractionofthechemicalenergyis‘lost’tofriction
andairresistance(i.e.,tothermalenergy)?Useanenergydensity
forgasolineof3107J/L.
1
Question6.NeutronStars
TheSunrotatesonitsaxisoncepermonth.IftheSunshrinksand
becomesaneutronstar,bywhatfactorwillitsrotationalinertia
change?Whatwillitsnewperiodofrotationbe?(Note:the
densityoftheSuntodayisapproximately103kg/m3.)
Question7.SolarMassLossandOrbits
AstheSunconvertshydrogentoheliumthroughnuclearfusion,it
emitsenergy.ThisdecreasesthemassoftheSunandchangesthe
orbitsofalltheplanets.HowmuchlighterwilltheSunbewhen
itcompletesthehydrogenburningphase?Byhowmuchwillthis
changetheorbitoftheEarth?Giveyouranswersinnumbersand
inpercent.
Question8.DriftingContinentMomentum
Whatisthemomentumofadriftingcontinent?(Estimatethis
inthereferenceframeoftheEarth;i.e.,ignoretherotationaland
translationalmotionoftheEarth.)Howdoesthiscomparetoa
supertankeroraircraftcarrie