Angular Momentum



1)††††††† An object with more† _______________________† will be more difficult to spin, but once it gets spinning it will be harder to stop.



2)††††††† A(n)† _______________________† is needed to change an objectís rotation.



3)††††††† Moving an objectís mass farther from its rotational axis increases its† _______________________† .



4)††††††† Imagine you were to look down upon a spinning childís toy, and it is rotating counter-clockwise. What is the direction of its angular velocity? If the toy were slowing in its rotation, what direction is its angular acceleration?





5)††††††† If a ball spins 3.0 times in 1.2 seconds, what is its angular speed? Give your answer in both rotations/second and radians/second.







6)††††††† A solid disc has a moment of inertia equal to (1/2)MR2. If a disc with a radius of 0.35 m and a mass of 0.95 kg spins 2.0 times in 0.75 seconds, what is its angular momentum? Assume itís spinning clockwise in a horizontal plane, and be very careful with your units.











7)††††††† Take the disc from Problem 6 and decrease its radius by half while it is spinning. If there are no external torques, what is its new angular velocity?





8)††††††† A neutron star forms when the remains of a massive star collapses after a supernova explosion. Before collapse, the star has a radius of 7 ◊ 108 m. After collapse it has a radius of 104 m. If the initial angular speed is 7.3 ◊ 10-6 radians/second, what is the angular speed after the collapse? The mass is the same before and after collapse. Model the rotating star as a uniform sphere Ė so its moment of inertia equals (2/5)MR2 Ė and be careful with precision.















9)††††††† Convert the speed found in Problem 8 from radians/second to rotations/second. Again, be careful with precision.







10)††††† Picture a vertical rotational axis. A 0.45 m horizontal lever is perpendicular to the axis, pointed east. Apply a 25 N force, due north. Calculate the torque. Donít forget the direction.