Acceleration vs Time Graph
The object has positive acceleration as it speeds up at the beginning of the journey. It has no acceleration as it travels at constant velocity in the middle of the journey. Its acceleration is negative as it slows down at the end of the journey.
Source
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"OpenStax College, College Physics. October 25, 2012."
http://cnx.org/content/m42100/latest/?collection=col11406/1.7
OpenStax CNX
CC BY 3.0.