12. A disk of radius R has a uniform charge density σ. It rotates about its central axis with the angular frequency ω. A uniform magnetic field B is normal to the axis. The torque on the disk is ______. (A)σωπBR⁴ (B) σωBR⁴ (C)σωπBR² (D) σωBR² (E) σωπBR⁴

2. The first stage of a Saturn V space vehicle consumes fuel and oxidizer at the rate of 1.50 × 10⁴ kg/s, with an exhaust speed of 2.60 × 10³ m/s. What is the acceleration of the vehicle just as it vertically lifts off the launch pad on the Earth if the vehicle's initial mass is 3.00 × 10⁶ kg? (A) 7.40 m/s² (B) 5.37 m/s² (C) 3.20 m/s² (D) 1.48 m/s² (E) None of the above is correct.

12. A disk of radius R has a uniform charge density σ. It rotates about its central axis with the angular frequency ω. A uniform magnetic field B is normal to the axis. The torque on the disk is ______.
(A)σωπBR⁴
(B) σωBR⁴
(C)σωπBR²
(D) σωBR²
(E) σωπBR⁴

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