5道世界上没人能都做出来的物理题,美国一所大学研究后公布的,英文的.美国一所大学研究后公布的,试试吧美国一所大学研究后公布的,试试吧1.Arollercoasterbeginswithasteepdownhilldescentfollowed

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5道世界上没人能都做出来的物理题,美国一所大学研究后公布的,英文的.美国一所大学研究后公布的,试试吧
美国一所大学研究后公布的,试试吧
1.A roller coaster begins with a steep downhill descent followed by a vertical loop.How
much higher does the initial hill have to be than the height of the loop so that the riders
experience a force of 1 G keeping them in their seats at the top of the loop.Assume
that the rolling friction involved is negligible.
2.A tower crane at a construction site covers a circle of radius 70 m.The mass of the
70 m long jib is 15,000 kg.To balance this mass at the top of the tower,
counterweights are suspended from a counter-jib which projects in the opposite
direction.
a) If the counter-jib is 22 m long and has a mass of 7500 kg,what mass of
counterweight is required at the end of the counter-b to balance the main jib.
b) Both jib sections are supported by cables which run to a section of the tower 9 m
above the level of the jib sections.What is the tension in each cable?
c) This crane has a maximum lifting capacity of 3,000 kg at a radius of 70 m.The
tower supporting the jib assembly is a square frame 2.6 m wide on each side.
Calculate the compression force on the side of the tower nearest the load and the
tension force on the far side of the tower,assuming that they are equally distributed
about the centre of the tower.
3.You are marooned on a desert island but,after some exploration,manage to find,in
surprisingly good condition,4 cases each containing a dozen 6 V lantern batteries.
Not far away you find a few 100 W floodlight bulbs.With some wire you decide to
make a device to signal in case a ship or airplane passes by at night.Unfortunately,
lantern batteries have an internal resistance; for these it is about 3 Ω.(Internal
resistance is a way of characterizing the ability of the battery’s chemicals to produce
current; it is the resistance of the circuit if no other elements are in it.) The light bulbs
have a DC resistance of about 9 Ω.
a) What configuration of batteries will give the brightest light from the bulb?(Hint:
think of connecting the batteries in a rectangular array of n rows and m columns.)
b) What are the chances of burning out the filament of the bulb?
c) Which will do a better job of signaling – pulsed or continuous light output?
4.A 10 mg sample of graphite (100% carbon) contains sufficient 14C to produce 16.6 β
particles in one day.If the half life of 14C is 5730 years,how many atoms of 14C are in
the sample?If you had obtained this information in order to determine the age of the
sample,how old would it be?(The contemporary abundance of 14C in carbon is about
1 14C atom in 1012 12C atoms.)
5.Titan,the largest satellite of Saturn has a radius of 2,575 km and a mass of 1.36 x 1023
kg.The NASA Cassini probe has measured its average surface temperature to be -
178°C.Which of the following gases would you expect to remain in the atmosphere of
Titan:ammonia,methane,helium or hydrogen?

Answer 1

好,既然做不出,分数给我吧.