Q9. Need help hard physics word problem

label Physics
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The tub within a washer goes into its spin cycle, starting from rest and reaching an angular speed of 16π rad/s in 7.2 s. At this point, the lid is opened, and a safety switch turns off the washer. The tub slows to rest in 16.7 s. Through how many revolutions does the tub turn? Assume constant angular acceleration while the machine is starting and stopping. Answer in units of rev

Oct 19th, 2017

Thank you for the opportunity to help you with your question! the solution is as such:

when the lid is opened, u= 16 π rad/s

final velocity v= 0 π rad/s 

we know, v= u + at                                 (here a denotes alpha for circular motion)

  so a = 0.95 π rad/s ^ 2


now v^2 = u^ 2 + 2aS

so, S= 134.7 π rads.

1 revolution require 2 π rads

so, this is equivalent to 134.7/ 2 = 67.3

so it will take almost 67 revolutions in stopping.


Please let me know if you need any clarification. I'm always happy to answer your questions.awaiting a positive feedback. thank you.
Jun 23rd, 2015

wrong answer :(

Jun 23rd, 2015

the concept is all correct, i am sad why are the answers not matching.

Jun 23rd, 2015

  • I have no idea, i was told this would be the hardest problem out of the 30

Jun 23rd, 2015

i tried to the best of  my knowledge.

Jun 23rd, 2015

hey its here


when the lid is opened, u= 16 π rad/s

final velocity v= 0 π rad/s 

we know, v= u + at  (here a denotes alpha i.e. acceleration for circular motion)

where t= 16.6s

  so a = 0.95 π rad/s ^ 2

now v^2 = u^ 2 + 2aS

so, S= 145.03 rads.

1 revolution require 2 π rads

so, this is equivalent to 145.03/2 so it will take almost 72.5 revolutions in stopping.


Jun 23rd, 2015

the previous mistake was that i was taking t= 16s

Jun 23rd, 2015

the technique looks correct but the computer still wont expect it

Jun 23rd, 2015

the technique looks correct but the computer still wont expect it

Jun 23rd, 2015

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Oct 19th, 2017
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