Rotational Motion And Angular Momentum Flashcards
Why do tightrope walkers carry a long narrow beam
The Beam gives the person a much greater distributed mass so a larger radius giving it a larger rotational inertia and therefore a harder time for the person to become unbalanced and rotate or fall, with the resistance in change the person has a greater time to recover in case he does fall
Two inclines have the same height but different angles with the horizontal, on whihc incline will teh speed of the ball at the ottom be greater
Since there is no friction teh energy is conserved adn teh mass is not a factor bc it will cancel out in teh math therefore the speed is independent of the angel of incline
Two solid spheres simultaneously start rolling from rest down an incline, one sphere has 2 times teh radius and 2 times the mass of the other, whihc reaches the bottom first, whihc has greater speed there, which has the greater kinetic energy at the bottom
Doing the math the speed has no dependence on the radius or mass because when teh height equals the total kinetic energy teh velocity is teh same bc not dependent on the mass or radius, for total kinetic energy the larger one has a greater KE bc of teh greater radius and mass adn therefore twice the KE
A sphere and a cylinder hve the same radius nad the same mss, they start from rest at the top of n incline which reaches the bottom first, whihc has the greter speed t the bottom, ne which has teh greter total kinetic energy a tht he bottom and greater rotational energy
Teh sphere bc it has a smaller rotational inertia so doesn’t take much to get it to start rolling and it gets to teh bottom first and has a greter speed t hte ottom, but they hve the same because same mass and radius, teh sphere cylinder has a greater rotational bc the rotational inertia is bigger
Suppose you are sitting on a rotating stool holding a 2 kg mass in each outstretched hand if you sudden ya bring your arms closer to your body will your angular velocity chang3, how will the angular momentum change, how
The angular velocity will increase bc the smaller radius and their smaller distribution of mass changing the rotational inertia making it smaller and easier to rotate, no bc it is conserved quantity
Two objects with same shape radius and mass will tehy reach bottom of ramp at the same time
No depends on where the weight is distributed if to the side teh distribution of mass is farther away therefore having a greater rotational inertia but if closer together then it rolls down faster
Two spheres look identical and have the same however one is hollow adn one is solid whihc one has more rotational inertia
Teh solid has smaller rotational inertia bc mass is greater to center so easier to get it rolling
Can a diver do a somersault without having any initial rotation when she leaves teh board explain how a diver could do a somersault
When start doing a somersault the body is rotating so angular momentum is conserved and tehy curl yp to change their moment of inertia so they can start to spin around faster, adn to have angular momentum to spin tehy have to have it before so tehy need to jump off an angle to get it and start rotating adn do a somersault
The moment of inertia of a rotating solid disk bout an axis through it center of mass is 1/2mr squared, suppose instead that teh axis of rotation passes through a point on the edge of the disk, will the moment of inertia be the same larger or smaller
Larger bc the mass is distributed further away so the moment of inertia is larger
Bonnie sits on the outer rim of a merry go round and jill sits midway between teh center and teh rim, the merry go round makes one complete revolution every 2 seconds Jill linear velocity is
Half of Bonnie’s bc they each travel a circumference in a same amount of trim but one is closer with a smaller circumference it will be half
An object t rest begins to rotate with a constant angular acceleration if this object rotated through Angle in time through what angle did it rotate in the time .5t
.25 angle bc it’s .5 times .5
Why is it more difficult to do sit ups with your hands behind tour back than when your arms re stretched out in front of you
The mass is distributed further away giving it a greater radius therefore a greater rotational intertidal making it harder for the person to start twisting and going up
