23.A dancer rotates herself 3 rounds per second at beginning and then increases the rotation frequency to 6 rounds per second. Assume the angular momentum is conserved. By how many times does the moment of inertia change?(A) 4 times (B) 2 times (C) 0.5 times (D) 0.25 times

1.In the figure shown on the right, a wire is extended from y = -(a+L) to y = a+L and is bent as a semicircle in the xy plane. If the wire carries a current I flowing along the direction indicated by the arrows and the magnetic flux density B in the region is along the +z direction, determine the magnetic force acting on the semicircular arc with the following parameters: I = 2 A, B = 5 T, a = 1 m, L = 2 m. (A) 10 Nt (B) 20 Nt (C) 30 Nt (D) 40 Nt (E) 5 Nt

23.A dancer rotates herself 3 rounds per second at beginning and then increases the rotation frequency to 6 rounds per second. Assume the angular momentum is conserved. By how many times does the moment of inertia change?
(A) 4 times
(B) 2 times
(C) 0.5 times
(D) 0.25 times

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