A neutron star is an extremely dense, rapidly spinning object that results from the collapse of a massive star at the end ofits life. A neutron star with 13 times the Sun's mass has an essentially uniform density of 4.8 x 1017 kg/ m3. (a) What's itsrotational inertia? (b) The neutron star's spin rate slowly de-creases as a result of torque associated with magnetic forces. Ifthe spin-down rate is 5.6 x 10-5 rad/s2, what's the magnitude of the magnetic torque?

Respuesta :

Answer:

(a). The rotational inertia is [tex]5.72\times10^{39}\ kg m^2[/tex]

(b). The magnitude of the magnetic torque is [tex]3.20\times10^{35}\ N-m[/tex]

Explanation:

Given that,

Mass of neutron [tex]M_{n}= 13M_{s}[/tex]

Density of neutron [tex]\rho=4.8\times10^{17}\ kg/m^3[/tex]

(a). We need to calculate the rotational inertia

Using formula of rotational inertia  for sphere

[tex]I=\dfrac{2}{5}MR^2[/tex]...(I)

We know that,

[tex]\rho=\dfrac{M}{V}[/tex]

Put the value of volume

[tex]\rho=\dfrac{3M_{n}}{4\pi R^3}[/tex]

[tex]R^2=(\dfrac{3M_{n}}{4\pi\rho})^{\frac{2}{3}}[/tex]

Put the value of R in equation (I)

[tex]I=\dfrac{2}{5}\times M_{n}\times(\dfrac{3M_{n}}{4\pi\rho})^{\frac{2}{3}}[/tex]

Put the value into the formula

[tex]I=\dfrac{2}{5}\times(13\times2\times10^{30})^{\frac{5}{3}}\times(\dfrac{3}{4\pi\times(4.8\times10^{17})})^{\frac{2}{3}}[/tex]

[tex]I=5.72\times10^{39}\ kg m^2[/tex]

The rotational inertia is [tex]5.72\times10^{39}\ kg m^2[/tex].

(b). We need to calculate the magnitude of the magnetic torque

Using formula of torque

[tex]\tau=I\times \alpha[/tex]

Put the value into the formula

[tex]\tau=5.72\times10^{39}\times5.6\times10^{-5}[/tex]

[tex]\tau=3.20\times10^{35}\ N-m[/tex]

The magnitude of the magnetic torque is [tex]3.20\times10^{35}\ N-m[/tex]

Hence, (a). The rotational inertia is [tex]5.72\times10^{39}\ kg m^2[/tex]

(b). The magnitude of the magnetic torque is [tex]3.20\times10^{35}\ N-m[/tex]