Answer
(a) $10^{3}~m/s$
(b) $10^{8}~m$
(c) $10^{7}~m$
Work Step by Step
See conversion factors (inside front cover).
(a) $3~h=3\times3600~s=10800~s\approx10^{4}~s$, $1~mi=1609~m$
$3000~mi=(3000~mi)(\frac{1609~m}{1~mi})\approx10^{7}~m$
$speed=\frac{distance}{time}=\frac{10^{7}~m}{10^{4}~s}=10^{3}~m/s$
(b) A day has $24~h=8\times3~h$. So, the circunference of the Earth is about $10\times10^{7}~m=10^{8}~m$ (equatorial line).
(c) $C=2πr$, where C is the circunference of the Earth and r the radius of the Earth. So:
$r=\frac{C}{2π}=\frac{10^{8}~m}{2π}\approx10^{7}~m$
