phy 201
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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:
v0 = 10 cm/s
vf = 20 cm/s
‘ds = 45 cm
‘dt = 2(‘ds)/(vf+v0) = 90/30 = 3 s
a = (vf-v0)/’dt = 10/3 = 3.33 cm/s^2
• 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:
v0 = vf – a(‘dt) = 50 – 10(3) = 20 cm/s
vf = 50 cm/s
‘ds = (‘dt*(v0+vf))/2 = (3*70)/2 = 105 cm
‘dt = 3 s
a = 10 cm/s^2
• A ball travels 30 cm along an incline, starting from rest, while accelerating at 20 cm/s^2.
answer/question/discussion:
v0 = 0 cm/s
vf = a(‘dt) = 10(1.732) = 17.32 cm/s
‘ds = 30 cm
‘dt = sqrt((2*’ds)/a) = sqrt(60/20) = 1.732 s
a = 10 cm/s^2
Then for each situation answer the following:
• Is it possible from this information to directly determine vAve?
answer/question/discussion:
1) yes
2) no, do not know ‘ds or v0
3) no, vAve = vf/2, but vf is unknown
• Is it possible to directly determine `dv?
answer/question/discussion:
1) yes
2) no, do know know ‘ds or v0
3) no, ‘dv = vf, but vf is unknown
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30 min.
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Good, but note that you can find `dv from a and `dt (second situation).