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Rotations, Angular Momentum

  • Thread starter forty
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Question:
A fighter pilot is being trained in a centrifuge of radius 15m. it rotates according to theta=0.25(t^3) + ln(t+1) befor it stabilises (theta in radians). what are the magnitudes of the pilots:

a) angular velocity: d(theta)/dt at t = 4 (12.2 rad/sec)

b) linear velocity: 12.2 * 15

c radial acceleration: 2nd derivative of theta=0.25(t^3) + ln(t+1) at t = 4 (5.96rad/sec^2)

d) tangential acceleration: 5.96 * 15

Are b and d just the angular values times the radius thats if a and c are right in the first place??


Thanks
 

Answers and Replies

tiny-tim
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Are b and d just the angular values times the radius thats if a and c are right in the first place??
Yes! :smile:

(v = rω and dv/dt = (d/dt)(rω) = r(dω/dt), since r is constant.)

But why was that worrying you? :confused:
 
135
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Because all the angular equivalents scare me!
 
tiny-tim
Science Advisor
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… just keep differentiating rθ …

Hi forty! :smile:

Just remember the definition of a radian: the angle whose arc-length = r.

And therefore generally:
tangential length = rθ.​

So (if r is constant), differentiate once for:

tangential speed v = rθ´ = rω

tangential acceleration a = rθ´´ = rω´. :smile:
(and of course radial acceleration = -rω² = -vω = -v²/r.)
 

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