No explain answer 5 and 7 5. When we apply the energy conversation principle to

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No

explain answer 5 and 7

5. When we apply the energy conversation principle to a cylinder rolling down an incline without sliding, we exclude the work done by friction because CA there is no friction present B) the angular velocity of the center of mass about the point of contact is zero the coefficient of kinetic friction is zero D the linear velocity of the point of contact (relative to the inclined surface) is zero E) the coefficient of static and kinetic friction are equal 6. A wheel, with rotational inertia I, mounted on a vertical shaft with negligible rotational inertia, is rotating with angular speed ao. A nonrotating wheel with rotational inertia 31 is suddenly dropped onto the same shaft as shown. The resultant combination of the two wheels and shaft will rotate at: A) 12 ax /3 3 ao /4 7. When a man on a frictionless rotating stool extends his arms horizontally, his rotational kinetic energy: must increases By must decrease C) must remain the same D) may increase or decrease depending on his initial angular velocity E) may increase or decrease depending on his angular acceleration

Explanation / Answer

5.- In this case, the point of contact is seen as an particle that is at rest just at that moment of time, and because of rolling down without sliding, the point does not change its velocity. At that moment the object act as a pivot.

7.- Because of rotational kinetic energy is directly proportional on the moment of inertia, and the moment of inertia is directly proportional of the square of distance between the particles and the rotational axis. At the moment he extends his arms, the distance increase, and the rotational kinetic energy MUST INCREASE.

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