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+3 votes
54.3k views
in Physics by (49.1k points)

A circular coil has moment of inertia 0.8 kg m2 around any diameter and is carrying current to produce a magnetic moment of 20 Am2. The coil is kept initially in a vertical position and it can rotate freely around a horizontal diameter. When a uniform magnetic field of 4 T is applied along the vertical, it starts rotating, around its horizontal diameter. The angular speed the coil acquires after rotating by 60° will be 

(1) 10 rad s–1 

(2) 10π rad s–1 

(3) 20 rad s–1 

(4) 20π rad s–1

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3 Answers

+1 vote
by (46.9k points)

Answer is (1) 10 rad s–1

+1 vote
by (25 points)
edited by

Ui + Ki  =  Uf + Kf

-MBcos60°+0 = - MBcos0° + 1/2​​​​​(Iw2​​​​​​) 

On solving the above equation, we get 

​​​​​​W = (MB/A)1/2   

      = 10.                             

+4 votes
by (22.8k points)

By energy conservation

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