Random physics question?

Question

A dollar bill is about 15.5 cm long. If seven trillion dollar bills were laid 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 about 6378 km.

Answer 1

     The first thing you want to do is achieve dimensional homogeneity (put everything in terms of the same units):

dollar bill length = .155 m

radius of earth  = 6378000 m

Next, solve for the circumference of the earth using the formula 2*pi*r:

earth diameter = (2)*(3.14)*(6378000) = 40,074,200 meters

Next, you want to find out the total length of seven trillion dollar bills layed end to end.  This would be (.155m) x (7,000,000,000,000) = 1,085,000,000,000 meters.  

Now you simply divide the total length by the circumference of the earth:

1,085,000,000,000 / 40,074,200= 27074.8 times

Answer: 27074.8 times

Answer 2

About 1068870 and a half.

Answer 3

(15.5*7,000,000,000,000)/(1,275,600*pi)

   1,275,600 is from turning the r into d and changing from cm to km. this should be around 27012867