## Example 1a and 1b, pg. 25 Physics and Math Content Review

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### Example 1a and 1b, pg. 25 Physics and Math Content Review

"Example 1a: Take north to be positive. A car is traveling south and speeding up. What is the sign of the acceleration?

Solution: Since the velocity vector points south and the car is speeding up, the acceleration vector must point south. With this sign convention, acceleration is negative.

Example 1b: Take north to be positive. A car traveling south speeds up from 10 m/s to 15 m/s in 10 s. What is its acceleration?

Solution: We write

a= -15 m/s - (-10 m/s)/10s = 0.5 m/s^2

This confirms our thinking in Example 1a."

To which I am confused. How can this "confirm our thinking in Example 1a" when the solution in 1a indicates that, by sign convention, acceleration is negative. Yet, the solution in 1b indicates that the acceleration is a positive 0.5 m/s^2. -15-(-10)/10 equals -0.5 not 0.5.
NS_Tutor_Andrew
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