# Is this velocity right?

1. Sep 14, 2008

### missie

Question: Look at figure 1.6. if Car a slowed to 30m/s. what would the velocity of car b relative to car a be?

figure 1.6 is a picture of 2 car going forward the same way. Car a is in the front and car b is in the back. Car a is going at 40m/s and car b is going 60 m/s.

will this be how i solve it?

40m/s - 60m/s = -20 m/s

is that how the answer is or i'm i wrong? is it another way?

2. Sep 14, 2008

### LowlyPion

But was that the actual question?

3. Sep 14, 2008

### missie

yes that was the question.

4. Sep 14, 2008

### missie

the problem is that i don't know if i solved it right.

5. Sep 14, 2008

### LowlyPion

6. Sep 14, 2008

### missie

30m/s - 60m/s = -30m/s

???? and thanks ;]

7. Sep 14, 2008

### LowlyPion

Not quite.

Take the vector difference by subtracting the vector of car A from the vector of Car B.

In the case where they were moving away the distance was getting bigger. Subtracting from the second really resulted in adding. In this case the vector of the second is larger and when you subtract the vector (of the one you want it relative to) it's not (-) it's (+). Reverse the order of the subtraction in the equation you gave.

8. Sep 14, 2008

### missie

thanks so much ;]