# Homework Help: A hard Physics Howework probelm

1. Oct 7, 2006

### asdfasdfwfv

Given that the diameter of the moon is
3,480 km, and using a meterstick plus a 25¢
coin or any flat round object, estimate the
distance, D, from the Earth to the Moon.
Need to provide labeled diagram and calculation. And
answer the question on next page.

How can you improve the accuracy of your measurement:
a.) decrease the length of the meterstick and increase
the diameter of the round object
b.) increase the length of the meterstick and increase
the diameter of the round object
c.) decrease the length of the meterstick and
decrease the diameter of the round object
d.) increase the length of the meterstick and decrease
the diameter of the round object

i been thinking about it for a while, and no idea how to do it... i need a diagram, and a short summary... any help would be appreciated. thanx!

2. Oct 7, 2006

### asdfasdfwfv

anyone knows?

3. Oct 7, 2006

### Andrew Mason

Can you configure your eye, quarter and moon to block the moon with the quarter? If so, can you draw a diagram of the moon, quarter, and eye in that configuration? That will give you a start.

AM

4. Oct 7, 2006

### asdfasdfwfv

what about the calcuation? iono what physics forumlas to use...

5. Oct 8, 2006

### Andrew Mason

No formulas here. You just have to figure it out. It has to do with geometry and similar triangles.

AM

6. Oct 8, 2006

### asdfasdfwfv

can u be more specific? what i hae to do with the meter stick though

7. Oct 8, 2006

### Andrew Mason

Draw a side view diagram of your eye and rays of light from the edges of the moon. Put the quarter between the eye and the moon so that the edges of the quarter touch the rays from the edge of the moon. Can you see similar triangles there? How is the distance from the eye to the quarter/diameter of the quarter related to the distance to the moon/diameter of the moon?

AM

8. Oct 8, 2006

### asdfasdfwfv

which one is the right anser, A-D??? thanx for helping :D

9. Oct 8, 2006

### Andrew Mason

AM

10. Oct 8, 2006

### Andrew Mason

The metre stick allows you to measure the distance from your eye to the quarter. How does $D_{25c}/L_{25}$ compare to $D_{moon}/L_{moon}$?

AM

11. Oct 8, 2006

### asdfasdfwfv

can i solove it by : place the coin in front of your eyes
adjust the position of the coin until the coin completely cover the Moon
measure the distance between your eyes and the coin, and measure the diameter of the coin
by finding the angle of inclination, the distance from the Earth to the Moon can be calculated.. the probelm is how do i find the angle of inclination????

12. Oct 8, 2006

### drpizza

So, you're holding the quarter so that it is at a right angle (perpendicular) to your line of site? Include that in your diagram.

13. Oct 8, 2006

### Andrew Mason

I am not sure what the difficulty is here.

You know that the angle of the moon/distance from moon to eye = angle of the quarter/distance from quarter to eye. You also know that the coin is parallel to the circle made by the moon. So you have similar triangles (1. made by the top and bottom of the coin and the eye and 2. made by the top and bottom of the moon and the eye). All you need to do is find is the ratio of the coin diameter to distance from the eye. That is the same as the diameter of the moon to the distance of the moon from the eye.

AM