Constant angular acceleration

  • Thread starter shadowice
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  • #1
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Homework Statement


A pulsar is a rapidly rotating neutron star that emits radio pulses with precise synchronization, there being one such pulse for each rotation of the star. The period T of rotation is found by measuring the time between pulses. At present, the pulsar in the central region of the Crab nebula has a period of rotation of T = 0.16000000 s, and this is observed to be increasing at the rate of 0.00000506 s/y.

If its angular acceleration is constant, in how many years will the pulsar stop rotating?
already found
angular acel to be -3.935x10^-11 rad/s^2
wf = 39.269
wi = 39.2699

Homework Equations





The Attempt at a Solution



Im stumped as to how to find this, i had initially tried to use wf = wi + angular accel*t thinking that the t i solved for would be the value i wanted.

i did 39.269 = 39.2699+ -3.935x10^-11t
that gave me 31559593.39 seconds then i did conversions to turn s into yrs which was that /60 s /60 min/24 hr/365d = 1.0007 yrs which is way to small it should be thousands of years shouldnt it.
 

Answers and Replies

  • #2
alphysicist
Homework Helper
2,238
1
Hi shadowice,

Homework Statement


A pulsar is a rapidly rotating neutron star that emits radio pulses with precise synchronization, there being one such pulse for each rotation of the star. The period T of rotation is found by measuring the time between pulses. At present, the pulsar in the central region of the Crab nebula has a period of rotation of T = 0.16000000 s, and this is observed to be increasing at the rate of 0.00000506 s/y.

If its angular acceleration is constant, in how many years will the pulsar stop rotating?
already found
angular acel to be -3.935x10^-11 rad/s^2
wf = 39.269
wi = 39.2699

Homework Equations





The Attempt at a Solution



Im stumped as to how to find this, i had initially tried to use wf = wi + angular accel*t thinking that the t i solved for would be the value i wanted.

i did 39.269 = 39.2699+ -3.935x10^-11t
that gave me 31559593.39 seconds then i did conversions to turn s into yrs which was that /60 s /60 min/24 hr/365d = 1.0007 yrs which is way to small it should be thousands of years shouldnt it.
I have not checked all your numbers here, but your two angular speeds you have are the angular speed at the initial point (wi) and one year later (wf). So when you calculated the time, you got back the original time of one year.

So instead, if we want to calculate the time when the pulsar stops, what angular speeds would be used in the equation?
 

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