• Sep 22nd 2008, 09:18 AM
Momo92
Please could you help me solve these two problems. I really can't do them. I just don't need the answer, but please I also need to know how to solve them.

Here:

As the moon orbits Earth the distance between them varies between 4.07 * 10^5 km and 3.56 * 10^5. Find the difference between these two distances.

The radius of Earth is approximately 6380 km. Find the volume of Earth in cm^3 giving your answer in standard forum correct to 3 significant figures. (use the formula V = 4/3 pii r^2)

Many thanks :)
• Sep 22nd 2008, 11:46 AM
earboth
Quote:

Originally Posted by Momo92
...
1. As the moon orbits Earth the distance between them varies between 4.07 * 10^5 km and 3.56 * 10^5. Find the difference between these two distances.

2. The radius of Earth is approximately 6380 km. Find the volume of Earth in cm^3 giving your answer in standard forum correct to 3 significant figures. (use the formula V = 4/3 pii r^2)

Many thanks :)

to #1:

Re-write the numbers:

$\displaystyle 4.07 \cdot 10^5\ km = 4.07 \cdot 100000\ km = 407000 \ km$

Do the same with the 2nd number and calculate the difference.

to #2:

Re-write 6380 km in cm:

$\displaystyle 6380\ km\cdot 1000 \dfrac{m}{km} \cdot 100 \dfrac{cm}{m} = 638000000\ cm$

Plug in this value into the formula:

$\displaystyle V_{sphere} = \frac43\cdot \pi\cdot r^\bold{\color{red}3}$
• Sep 23rd 2008, 10:36 AM
Momo92
Wow. Thanks so much :)