MIME-Version: 1.0 Content-Location: file:///C:/D9286902/Fall08.Phys2211.Quiz11.SolutionWeb.htm Content-Transfer-Encoding: quoted-printable Content-Type: text/html; charset="us-ascii" Department of Natural Sciences

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Department = of Natural Sciences

Clayton State University

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November 14, = 2008

Physics 221= 1 – Quiz 11

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Name  _____SOLUTION_______________________________

 

At t =3D 0 a grinding whee= l has an angular velocity of 24.0 rad/s. It has a consta= nt angular acceleration of 30.0 rad/s2 until a circuit breaker trips at t = =3D 2.00 s. From then on, it turns through 432 rad = as it coasts to a stop at constant angular acceleration.

 

a. Through what total angl= e did the wheel turn between t =3D 0 and the time it stopped?

 

Before the circuit breaker= trips:

qf =3D qi<= /sub> + wi t + ½ a t2

 

qf =3D (24.0 ra= d/s) (2.00 s) + ½ (30.0 rad/s2) (2.00 s)2<= /sup> =3D 108 rad

 

Until it stopped:

 

qf =3D 108 rad + 432 rad =3D 540 rad

 

b. At what time did it sto= p?

 

At the moment the circuit = breaker trips:

 

wf =3D wi<= /sub> + a t

 

wf =3D 84.0 rad/s

 

After it trips:

 

wi =3D 84.0 rad= /s

wf =3D 0

 

wf 2=3D wi 2+ a (Dq)

 

a =3D (wf 2 -= wi 2) / (Dq)

 

a =3D -8.17 rad/s2

 

t =3D (wf - wi )/ a  =3D 10.3= s

 

c. What was its accelerati= on as it slowed down?   

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a =3D -8.17 rad/s2