phy 121
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Asst 6 Question 1
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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
'ds= (v0+vf)/2 * 'dt
45 cm = (10 cm/s+20 cm/s)/2 * 'dt
45 cm = 15 cm/s * 'dt
3 s = 'dt
20 cm/s= 10cm/s +a*3s
10 cm/s = a*3s
3.33 cm/s/s =a
#$&*
*&$#
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: ->->->->->->->->->->->-> :
a=10 cm/s/s
'dt= 3 s
vf= 50 cm/s
50 cm/s= v0 + 10 cm/s/s* 3 s
50 cm/s = v0 + 30 cm/s
20 cm/s =v0
'ds= (20 cm/s + 50 cm/s)/2 * 3s
'ds = 35 cm/s* 3 s
'ds= 105 cm
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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: ->->->->->->->->->->->-> :
'ds= 30 cm
v0= 0 cm/s
a= 20 cm/s/s
'ds=v0'dt+.5a'dt^2
30 cm=0+ .5(20cm/s/s)dt^2
30 cm=0+ 10 cm/s/s(dt^2)
3s/s= dt^2
1.73s ='dt
vf=v0 + a*'dt
vf=0cm/s +20 cm/s/s(1.73s)
vf= 34.6 cm/s
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Then for each situation answer the following:
Is it possible from this information to directly determine vAve?
answer/question/discussion: ->->->->->->->->->->->-> :
Yes, it definitely is because one can use the equation 'ds=vAve * 'dt
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Is it possible to directly determine `dv?
answer/question/discussion: ->->->->->->->->->->->-> :
Yes, using the equation 'dv=a* 'dt
#$&*
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