# Homework Help: Wat does my teacher want me to do?

1. Nov 3, 2005

### DB

hey guys, im a lil confused with this one, not really with the concept, just how to start...
4) a snowmobile is being driven across a frozen lake. Vector V1 and Vector V2 in the diagram represents its velocity at two instants 3 s apart. 1 cm = 5 m/s
Determine $$\overrightarrow{\Delta V}$$ and the average acceleration.

i know i have to find the vector difference in v2 and v1 and the divide that by change in time but in the diagram all the teacher did was draw 2 lines (vectors) without an angle or a line showing where 180 degrees is, and just labeled them v1 and v2. how do i do the vector subtraction? i know i have to put them tail to tail, but how do i do it without knowing wat the angles are?

2. Nov 3, 2005

### James R

You need the angle if you're going to be able to work out the magnitude of the difference between the two vectors, unless you're doing this using a scale diagram.

3. Nov 3, 2005

### DB

i think we are using a scale diagram, it says 1 cm = 5 m/s, is that wat u mean?

4. Nov 3, 2005

### Chi Meson

It's been a while, so I'll say, "yes" it's what he means. When finding the delta V, the difference between two vectors is the arrow that goes from the tip of the first vector to the tip of the second vector. This is vector subraction. Notice that if you do this in the wrong order, you get the opposite-pointing vector.

5. Nov 4, 2005

### James R

DB:

Yes, with the given scale, you should be able to do the vector subtraction on the diagram, and read off the length of the resulting vector directly from the diagram.