# Physics Question

• Sep 26th 2012, 12:17 PM
Louisana1
Physics Question
A car traveling westward at 20 m/s turns around and travels eastward at 15 m/s. If this takes place in 5 s, what is the average acceleration of the car?
15-20= -5= -1
5 5

Is this worked correctly
• Sep 26th 2012, 07:05 PM
johnsomeone
Re: Physics Question
No, you have an error with your signs.
Let's say the eastward direction is the positive direction. Let's demand units of meters and seconds everywhere.

Then the problem says $v_i = -20, v_f = 15$ at times $t_i = 0, t_f = 5$.

Thus the average acceleration over those 5 seconds is given by:

$a_{ave} = \frac{v_f - v_i}{t_f - t_i} = \frac{(15) - (-20)}{(5) - (0)}= \frac{15 + 20}{5}= \frac{35}{5} = 7$.

Thus the average acceleration over those 5 seconds was 7 meters per second squared.