Assumed Values

In physics story problems, there are often assumed values that are hidden in the story. They are a word, phrase, or implied idea that is supposed to give you a number to be used in your equations. 

For motion in one dimension: 

• Starting or ending from rest:  vi or vf = 0m/s
• If something is dropped:  vi=0m/s
• If something gets the the maximum height:  vf = 0m/s (it's not moving up or down at the top of the flight)
• If you are on earth going up and down: a=9.8 or 9.80m/s/s

For 2D motion:

This means ax=0m/s/s while ay=9.8m/s/s

The speed at the top is only the horizontal component