正確回答三道就可以給分
Question 1.How many people are talking on their cell phones at this instant?
Question 2.How large a moon can you jump off of?
In other words,assuming reasonable densities,what is the radius of
the largest rocky sphere from which you can reach escape velocity
by jumping?Estimate your answer within a factor of 10.
Question 3.Acceleration
Estimate and compare the accelerations of a) a jet airplane taking
off,b) a car accelerating to highway speed,and c) a person starting
on a walk.
Question 4.Stop the World,I Want to Get off
If every human ran for 10 seconds as fast as possible to the east,
by what fraction would they change the Earth’s angular velocity
around its axis (while they were running)?
Question 5.Automobile kinetic energy
Compare the kinetic energy of a car driving on the highway with
the chemical energy required to keep driving for one minute and for
one hour.What fraction of the chemical energy is ‘lost’ to friction
and air resistance (i.e.,to thermal energy)?Use an energy density
for gasoline of 3 107 J/L.
1
Question 6.Neutron Stars
The Sun rotates on its axis once per month.If the Sun shrinks and
becomes a neutron star,by what factor will its rotational inertia
change?What will its new period of rotation be?(Note:the
density of the Sun today is approximately 103 kg/m3.)
Question 7.Solar Mass Loss and Orbits
As the Sun converts hydrogen to helium through nuclear fusion,it
emits energy.This decreases the mass of the Sun and changes the
orbits of all the planets.How much lighter will the Sun be when
it completes the hydrogen burning phase?By how much will this
change the orbit of the Earth?Give your answers in numbers and
in percent.
Question 8.Drifting Continent Momentum
What is the momentum of a drifting continent?(Estimate this
in the reference frame of the Earth; i.e.,ignore the rotational and
translational motion of the Earth.) How does this compare to a
supertanker or aircraft carrier at top speed?
Question 9.Dynamic Range of the Eye
What is the dynamic range of the human eye?In other words,
what is the ratio of the maximum power that can be seen without
damaging the eye to the minimum power that can be perceived?
(Hint:The energy of one photon is given by E = h_,h is the planck
constant.)
Question 10.Satellite Data
Google Maps currently supplies satellite photographs of Earth with
a resolution of a few meters.How much disk space is needed to store
all that data?If they improve the resolution to 1 cm,how much
more disk space will be needed?How much data transmission rate
will be needed if they update the photographs annually?
Question 11.Lecture Hall:Mass of Brain vs Mass of Air
Compare the mass of air with the mass of brains contained in the
typical lecture hall.