Monday
March 30, 2015

Homework Help: science (conversion)

Posted by ~christina~ on Friday, September 14, 2007 at 11:31pm.

At the time of this books printing the national debt is about $8 trillion.
(a) If payments were made at the rate of $1000 per second, how many years would it take to pay off the debt, assuming no interest were charged?

(b)A dollar bill is about 15.5cm long. If 8 trillion dollar bills wre layed end to end around the earth's equator, how many times would they encircle the planet? Take the radius of the Earth at the equator to be 6,378km

I just can't get the answer I get for problem a to match the answer at the back of the book (250yrs)

~my work and thoughts on this:
60s= 1min
60min= 1hr

24hr= 1day so
60min*24hr= 1,440min in 1 day

-I'm not sure about the days in a year though since an example in the book takes into account leap years as 400days in a year but I know that it's usually 365 days in a year so I'll use that unless someone says otherwise.

1,440min in a day..
1,440min*365days= 525,600 min in a yr

now since I have minutes in a year I convert the rate of $1000/sec to how much in a year.

($1,000/sec)(60sec/min)(525,600min/yr)=
$3.1536e10/yr

now 8 trillion is 8e12 so..

($3.1536e10/yr)($8e12/ x yr)= 253.68 yrs

- I don't know why I got 3 years more than the book.

(b)know: radius of earth at equator = 6,378km
dollarbill length= 15.5cm

c=2pi*r
c= 2*pi*6,378km= 40,074.15589km (circumfrence of earth)

15.5cm(1in/2.54cm)(1m/39.3700787in)(1000km/1m)= 1.550e-4km

40,074.15589km/1.550e-4km = 258542941.2/ 3.0e9

answer given by book: 3.09e4 times

Again so close but not exactly what I got..I don't know what's the problem.

Can anyone help?
Thanks =)

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