force in relation to angular momentum


by valvan1
Tags: angular, force, momentum, relation
valvan1
valvan1 is offline
#1
Oct28-10, 02:11 AM
P: 3
so a student is sitting on a spinning stool and has a 2kg dumbbell in each hand angular velocity is 3rad/sec arms stretched out is a radius of 80cm and he pulls in his arms to 20cm. for this problem your ignoring the students weight.

from other problems i have figured out
so angular velocity to start with is 3 rad/sec
angular velocity final is 48 rad/sec

kinetic energy initial is 11.52( dont know what dimensions this is im guessing J)
kinetic energy final is 184.32

and i need to find the force required to pull on of the dumbells in at a constant speed is equal to F=((initial angular momentum of 1 block)^2)/(4*Mass of one weight*Radius^3)) or do i use the change in kinetic energy equation ?

do i say Torque=F*d and Torque=I*alpha and then go Force = Ia/d? or is there another way to solve this that im not seeing ?
Phys.Org News Partner Physics news on Phys.org
Physicists design quantum switches which can be activated by single photons
'Dressed' laser aimed at clouds may be key to inducing rain, lightning
Higher-order nonlinear optical processes observed using the SACLA X-ray free-electron laser
valvan1
valvan1 is offline
#2
Oct28-10, 02:54 AM
P: 3
sorry i posted it again in the homework section so you can delete this one, sorry about that


Register to reply

Related Discussions
The relation between angular and linear momentum Classical Physics 4
commutation relation of angular momentum Advanced Physics Homework 3
Relation between angular momentum and total engery Advanced Physics Homework 0
angular momentum and newtons' law relation Classical Physics 18
centripetal force relation to angular momentum Introductory Physics Homework 1