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Finding the total acceleration

  • #26
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but the answer does not match up with the answers possible.
 
  • #27
SammyS
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but the answer does not match up with the answers possible.
What are the possible answers ?
 
  • #28
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What are the possible answers ?
1.4 , 2.99 , 4.39 , 4.60 , and 5.78
 
  • #29
SammyS
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Oh !!! I see what went wrong.

It takes longer than 7.5 s for the first 1/4 of a lap.

Base the angular acceleration on one complete lap.

ωf = 2ωavg = 2(2π)/30 .

Angular acceleration, α = (ωf-0)/30 . That's 1/4 of the former answer.
 
  • #30
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Oh !!! I see what went wrong.

It takes longer than 7.5 s for the first 1/4 of a lap.

Base the angular acceleration on one complete lap.

ωf = 2ωavg = 2(2π)/30 .

Angular acceleration, α = (ωf-0)/30 . That's 1/4 of the former answer.
i am abit confused
 
  • #31
SammyS
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  • #32
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Confused about what in particular ?

ωf = 2ωavg = 2(2π)/30 .

Angular acceleration, α = (ωf-0)/30 . That's 1/4 of the former answer.
 
  • #33
SammyS
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ωf = 2ωavg = 2(2π)/30 .

Angular acceleration, α = (ωf-0)/30 . That's 1/4 of the former answer.
What you didn't include from that post was:
Base the angular acceleration on one complete lap.
All I did in the above QUOTE'ed text was to repeat what we had previously done, but used a complete lap since for a complete lap, we know the elapsed time. Once you have this value, you will need to find the velocity at the 1/4 lap point so that you can recalculate the radial component of acceleration, since that is also wrong.

Do you know the kinematic equations for constant angular acceleration?




If you work everything out, you would find that using our previous answer for angular acceleration, π/7.5/7.5, one lap would take only 15 seconds.
 
  • #34
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What you didn't include from that post was:
Base the angular acceleration on one complete lap.
All I did in the above QUOTE'ed text was to repeat what we had previously done, but used a complete lap since for a complete lap, we know the elapsed time. Once you have this value, you will need to find the velocity at the 1/4 lap point so that you can recalculate the radial component of acceleration, since that is also wrong.

Do you know the kinematic equations for constant angular acceleration?




If you work everything out, you would find that using our previous answer for angular acceleration, π/7.5/7.5, one lap would take only 15 seconds.
i do not know how to find the
constant angular acceleration
 
  • #36
SammyS
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i am getting 4.60
Yes.

Notice, that's 2/4 of your previous answer. :smile:
 

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