physics_randomprob1

#$&*

course phy121

2/3/2013 6

1.If the velocity of the object changes from 2 cm / sec to 10 cm / sec in 10 seconds, then at what average rate is the velocity changing?2.A ball rolling from rest down a constant incline requires 6 seconds to roll the 61 centimeter length of the incline.

What is its average velocity?

3.An object which accelerates uniformly from rest will attain a final velocity which is double its average velocity.

What therefore is the final velocity of this ball?

What average rate is the velocity of the ball therefore changing?

4.An automobile accelerates uniformly down a constant incline, starting from rest. It requires 9 seconds to cover a distance of 124 meters. At what average rate is the velocity of the automobile therefore changing?

Answer:

1. (10-2) /10= 8/10 =.8 cm/ seconds

@&
The appropriate calculation is not

(10-2) /10

but rather

(10 cm/s - 2 cm/s) /(10 sec).

The result does not come out with units of cm/s.

Do the algebra of the units.

Your .8 is the correct number.
*@

2. 61 cm/6 sec= 10.166 cm/ sec

3. final velocity= 10.166*2= 20.332

@&
what are the units of this result?
*@

average rate=(0+20.322)/2=10.166 cm/sec

@&
This is the average velocity, but it's not the average rate at which the velocity is changing.
*@

4.124m / 9 seconds =13.777 m/sec

@&
This is (change in position) / (change in clock time), which is the average rate of change of position with respect to clock time, or the average velocity.

This is useful but it's not the average rate of change of velocity with respect to clock time.

You've got a good start on this question, but you need to clearly identify your quantities. See the above for the necessary sequence of reasoning.
*@

@&
You're doing a lot of good things here, but you need to use units throughout, and need to identify your quantities carefully.

See what you can do with a revision, and we'll go from there.

&#Please see my notes and submit a copy of this document with revisions, comments and/or questions, and mark your insertions with &&&& (please mark each insertion at the beginning and at the end).
Be sure to include the entire document, including my notes.

physics_randomprob1

@& The appropriate calculation is not (10-2) /10 but rather (10 cm/s - 2 cm/s) /(10 sec). The result does not come out with units of cm/s. Do the algebra of the units. Your .8 is the correct number. *@

@& what are the units of this result? *@

@& This is the average velocity, but it's not the average rate at which the velocity is changing. *@

@& You're doing a lot of good things here, but you need to use units throughout, and need to identify your quantities carefully. See what you can do with a revision, and we'll go from there.

&#Please see my notes and submit a copy of this document with revisions, comments and/or questions, and mark your insertions with &&&& (please mark each insertion at the beginning and at the end).Be sure to include the entire document, including my notes.

@&
The appropriate calculation is not

(10-2) /10

but rather

(10 cm/s - 2 cm/s) /(10 sec).

The result does not come out with units of cm/s.

Do the algebra of the units.

Your .8 is the correct number.
*@

@&
what are the units of this result?
*@

@&
This is the average velocity, but it's not the average rate at which the velocity is changing.
*@

@&
You're doing a lot of good things here, but you need to use units throughout, and need to identify your quantities carefully.

See what you can do with a revision, and we'll go from there.

&#Please see my notes and submit a copy of this document with revisions, comments and/or questions, and mark your insertions with &&&& (please mark each insertion at the beginning and at the end).
Be sure to include the entire document, including my notes.