In 2003, the U.S. national debt was about $7 trillion. (a) Ifpayments were made

Question

In 2003, the U.S. national debt was about $7 trillion. (a) Ifpayments were made at the rate of $1 000 per second, how many yearswould it take to pay off the debt, assuming that no interest werechanged? (b) A dollar bill is about 15.5 cm long. If seven trilliondollar bills were laid end to end around the Earth's equator, howmany times would the encircle the planet? Take the radius of theEarth at the equator to be 6 378 km. (Note: Before doingany of these calculations, try to guess at the answers. You may bevery surprised.)

Explanation / Answer

a) $7 trillion =$1*1012 time take T = 1*1012 / $1000 (s) = 1*109s = 1*109 / (3600*24*365) (years) = 31.7 years˜ 32 years b) one dollar length is 15.5cm = 0.155 m the total length of the $7 trillion is: L = 1*1012*0.155m = 1.55*1011m the circonference of the earth is: L1 = 2r = 2*3.14*6378*1000 m =4.005384*107m L/L1 = 3869.8 it is 3869.8 times encircle the planet.

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