#$&*

course Phy 231

2-2-11 about 12:00am

The problem:A ball starts with velocity 4 cm/sec and ends with a velocity of 10 cm/sec.

• What is your best guess about the ball's average velocity?

answer/question/discussion: ->->->->->->->->->->->-> (start in the next line): 

&&&&

(10cm/sec + 4cm/sec)/2= 7cm/sec

&&&&

#$&*

• Without further information, why is this just a guess?

answer/question/discussion: ->->->->->->->->->->->-> (start in the next line): 

&&&&

There is no time interval given, no initial or final time given

&&&&

@& Average velocity is half of final velocity provided initial velocity is zero.

However this is not the definition of average velocity, and the special case of initial velocity equal to zero is not satisfied here.

You always need to start out with the most basic definition, and apply special cases with care to be sure that they do apply.*@

#$&*

• If it takes 3 seconds to get from the first velocity to the second, then what is your best guess about how far it traveled during that time?

answer/question/discussion: ->->->->->->->->->->->-> (start in the next line): 

&&&&

ds= 7cm/sec * 3sec= 21cm

&&&&

#$&*

• At what average rate did its velocity change with respect to clock time during this interval?

answer/question/discussion: ->->->->->->->->->->->-> (start in the next line): 

&&&&

(10cm/sec – 4cm/sec)/3sec= (6cm/sec)/3sec= 2cm/sec/sec

&&&&

#$&*

** **

20 min

** **

@& None of your answers appear to be correct.

You have only explained in one question how you got the answer.

You need to reason your answers out, starting with the basic definition of average rate of change.

Please rework and resubmit this exercise.*@