# Average Acceleration Question

1. Mar 11, 2014

### a.k

1. The problem statement, all variables and given/known data
A motorboat traveling in a straight line has a velocity of +4.0 m/s at some point in time. After 5.0 seconds, its velocity is +7.0 m/s. What is its average acceleration during this time?

2. Relevant equations

avg accel.=change in velocity/change in time

3. The attempt at a solution

7.0 m/s-4.0 m/s=3.0 m/s

$\frac{3 m/s}{5s}$

0.60 m/s^2.

I dont understand why is it m/s^2 versus m/s. What does the plus sign indicate in the question in front of 7.0 and 3.0?

2. Mar 11, 2014

### jackarms

Well, $\frac{m}{s^{2}}$ is just the unit of acceleration. When you have $\frac{m}{s}$, then divide that by a time, then the denominator becomes $s^{2}$. And the plus sign is just used to indicate the direction of the velocity, and to indicate that the boat travels in a straight line.