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Phy 231

For each situation state which of the five quantities v0, vf, `ds, `dt and a are given, and give the value of each.

A ball accelerates uniformly from 10 cm/s to 20 cm/s while traveling 45 cm.

answer/question/discussion: ->->->->->->->->->->->-> :

Given v0, and vf, you can find vave to be (20+10)/2 = 15m/s

Once that is found, you can find 'dt: 'dt = 'ds/vave = 45/15 =3m/s

Then you can find a by: (20-10)/3 = 3.33 m/s^2

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A ball accelerates uniformly at 10 cm/s^2 for 3 seconds, and at the end of this interval is moving at 50 cm/s.

answer/question/discussion: ->->->->->->->->->->->-> :

YOu know a, 'dt, and vf. You can find 'dv: 'dv = a * 'dt = 10 * 3 = 30 m/s

To find vf, vf ='dv + v0 = 30 + 50 = 80 cm/sec

Now you can find vave = (80 + 50)/2 = 65 m/s

Next, you can find 'ds = vave * 'dt = 65 * 3 = 195 meters

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A ball travels 30 cm along an incline, starting from rest, while accelerating at 20 cm/s^2.

answer/question/discussion: ->->->->->->->->->->->-> :

You can use the third motion equation: 'ds = v0 * 'dt + .5 * a * 'dt^2

30 = 0 * 'dt + .5 * 20 * 'dt^2

'dt = 1.73 sec

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Then for each situation answer the following:

Is it possible from this information to directly determine vAve?

answer/question/discussion: ->->->->->->->->->->->-> :

In the first question you could find vave from v0 and vf.

In the second, you could find vave after finding the final velocity

Finally, the third one can be found using the equations for motion

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Is it possible to directly determine `dv?

answer/question/discussion: ->->->->->->->->->->->-> :

The first could be found from being given v0 and vf.

The second could be found from known 'dv and a.

THe third can be found using the equations of motion.

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