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The Earth is 1.51011m from the Sun and takes a year to make one complete orbit. It rotates on its own axis once per day. It can be treated approximately as a uniform-density sphere of mass61024kg and radius6.4106m (actually, its center has higher density than the rest of the planet and the Earth bulges out a bit at the equator). Using this crude approximation, calculate the following: (a) What isvCM ? (b) What isKtrans ?(c) What is , the angular speed of rotation around its own axis? (d) What isKrot ? (e) What isKtot ?

Short Answer

Expert verified
  1. The value of vCMis,2.95104m/s.
  2. The value of Ktransis, 2.611033J.
  3. The angular speed of rotation is, localid="1657948862975" 7.2710-59rad/s.
  4. The value of Krotis, 2.6102J.
  5. The value ofKtotis,2.611033J.

Step by step solution

01

Identification of the given data

The given data can be listed below as,

  • The earth distance from sun is,r=1.51011m .
  • The mass of earth is,M=61024kg
  • The radius of the earth is,R=6.4106m
02

Significance of kinetic energy

The Kinetic energy is the form of energy that an object or particle retains due to its motion.

03

(a): Determination of the vcM

The relation of angular speed of revolution is expressed as,

rev=2Trev ...(i)

Hererav is the angular speed of revolution, andTrevis the period of revolution.

Trev=365d24hr3600s=31.536106s

Substitute the value ofTrevin the equation (i).

rev=231.536106s=1.9910-7red/s

The relation of velocity relative to the center of mass is expressed as,

vCM=r蝇rev ...(ii)

Here r is the radius of orbit around the sun.

Substitute 1.9910-7red/s for rev, and1.51011mfor r in the equation (ii).

role="math" localid="1657946164781" vcM=1.51011m1.9910-7red/s=2.95104m/s

Hence the value of vcM is,2.95104m/s. .

04

(b): Determination of the Ktrans

The relation of translation kinetic energy is expressed as,

Ktrans=12Mv2CM ...(iii)

Here Ktrans is the translation kinetic energy and M is the mass of earth.

Substitute 2.95104m/s forvCM , and61024kgfor M in the equation (iii).

Ktrans=1261024kg2.95104m/s2=2.611033J

Hence the translation kinetic energy is, role="math" localid="1657946745049" 2.611033J.

05

(c): Determination of the angular speed of rotation around its own axis, ωrot

The relation of angular speed of rotation is expressed as,

rot=2Trot ...(iv)

Hererotis the angular speed of rotation, andTrotis the period of rotation.

Trot=24hr3600s=8.64104s

Substitute the value ofTrotin the equation (iv).

rot=28.64104s=7.2710-5rad/s

Hence the angular speed of rotation is,7.2710-5rad/s .

06

(d): Determination of the  Krot

The relation of kinetic energy associated with rotation of the object is expressed as,

Krot=12I蝇2rot ...(v)

HereKrot is the kinetic energy associated with rotation of the object, andlis the moment of inertia.

The moment of inertia of the sphere is expressed as,

I=25MR2

Substitute the value oflin the equation (v).

Krot=1225MR22rot=15MR22rot

Substitute 7.2710-5rad/sforrot,61024kgforand6.4106mforRin the above equation.

Krot=1561024kg6.4106m27.2710-5rad/s2=2.61029J

Hence the kinetic energy associated with rotation of the object is, .

07

(e): Determination of the Ktot

The relation of the total kinetic energy is expressed as,

Ktot=Ktrans+Krot ...(vi)

Substitute the value of Ktrans and Krot in the equation (vi).

Ktot=2.611033J+2.61029J=2.611033J

Hence the total kinetic energy is,2.611033J .

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