Choices: increases, decreases, stays the same, or undetermined. a) You are stand

Question

Choices: increases, decreases, stays the same, or undetermined.   

a) You are standing at the center of a large freely rotating platform. As you walk toward the edge of the platform, the rate of rotation of the platform __________.

b) You are standing on a rotating chair holding a 2-kg dumbbell in each hand close to your chest. When you move the dumbbells outwards, the rotational kinetic energy _________.

c) Two equal masses, m1 and m2, are on a turning wheel at a distance R from the axis of rotation. When the masses are moved to 2R, the angular momentum of the masses _________. ( the wheel turns without any friction.)

d) Two equal masses, m1 and m2, are on a rotating rod of negligible mass at a distance R from the axis of rotoation. When the masses are moved to 2R without exerting external torque, the linear velocity of masses ________.

e) You are sitting on a rotating chair holding a 2-kg mass each in your outstretched arms. When you drop the masses, your angular velocity _______.

Explanation / Answer

(a) Increases since the angular momentum is conversed, this means as the moment of intertia decreases, the angular velocity of the plat form increases.

(b) Decreases, again angular momentum is conversed. Iw=constant so rotational KE = 1/2Iw^2=(Iw)^2/(2I) so the Rotational KE is inversly proportinal to Moment of intertia. As I will increase, KE will decrease.

(c) Increases External work needs to be done to move out the masses. So angular momentum increases.

(d) Decreases As the angular momentum of the systtem remians constant

(e) Increases by conservation of angular momentum.

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