# Homework Help: Reference frames

1. Feb 11, 2008

### portillj

A car travels due east with a speed of 35.0 km/h. Raindrops are falling at a constant speed vertically with respect to the Earth. The traces of the rain on the side windows of the car make an angle of 65.0° with the vertical. Find the velocity of the rain with respect to the following reference frames.
(a) the car
(b) the Earth

I tried to solve the problem by putting it in a pythagorean model.... 35/cos(65) but it did not work.... HELP

2. Feb 11, 2008

### lavalamp

The angle of the rain is along the hypotenuse of the triangle, and it is 65 degrees from the vertical side of length 35. Since you want to find the length of the side opposite the angle, and you have only the adjacent side length, you need to use tan.

3. Feb 11, 2008

### portillj

How would the triangle would look!? i get confused when it says 65degrees from the vertical side of length 35

4. Feb 11, 2008

### _Mayday_

With these questions it's usually best to draw out a small sketch to visualise what is happening.

5. Feb 11, 2008

### portillj

wat does it mean with 65 degrees from the vertical side of length 35??? how does tat affect the triangle

6. Feb 11, 2008

### _Mayday_

Draw a base line that represents the length of 35, then from that sketch a line 60 degrees from that base.

7. Feb 11, 2008

### portillj

i was told to use tan to find the answer!! but i dont have the opposite side? also wat's the difference btw the car and the earth

8. Feb 11, 2008

### lavalamp

Heh, oops, may have given you a spot of bad advice there. I thought you needed to find the velocity of the car, which is what using tan would get you.

You were right with what you had before. That would tell you the resultant velocity of the rain relative to the car.

With respect to the Earth, the question has already said that the rain is falling vertically downwards at 35 Km/h, so I dunno, I guess that's just it.

9. Feb 11, 2008

### portillj

i was not able to get the answer for the first one and well the earth i got it wrong!!!!!

10. Feb 11, 2008

### _Mayday_

Portillj show us some of your working.