- #1
cjavier
- 17
- 0
So...I have two different homework problems. I'm not asking for answers to these problems! Just clarification. In problem one I am asked: A thin disk with diameter d rotates about an axis through its center with 0.260J of kinetic energy.What is the speed of a point on the rim? I use E = 1/2Iω2 for kinetic rolling energy.
THEN I am told by chegg.com, which provided the correct answer, to use v=ωr to find the tangential speed, or the speed of a point at the edge of the disk. Keep in mind, this disk is not moving transitionally, only spinning.
In problem two: I am given a problem that needs me to find the energy of a rolling sphere when it reaches the bottom of the hill. When I use Ef = KErolling + KEtransitional I receive this equation:
Ef = 1/2Iω2 + 1/2mvCM2.
THIS IS THE CONFUSING PART, CHEGG TELLS ME TO REPLACE vcenter/mass with ωr.
Why am I able to do this? From my first homework problem, I established that v is equal to the speed at the tip of the rotating object. By replacing v with ωr for my kinetic energy, I am now saying that the transitional energy is dependent on the speed at the tip of the sphere!
Dazed and Confused
THEN I am told by chegg.com, which provided the correct answer, to use v=ωr to find the tangential speed, or the speed of a point at the edge of the disk. Keep in mind, this disk is not moving transitionally, only spinning.
In problem two: I am given a problem that needs me to find the energy of a rolling sphere when it reaches the bottom of the hill. When I use Ef = KErolling + KEtransitional I receive this equation:
Ef = 1/2Iω2 + 1/2mvCM2.
THIS IS THE CONFUSING PART, CHEGG TELLS ME TO REPLACE vcenter/mass with ωr.
Why am I able to do this? From my first homework problem, I established that v is equal to the speed at the tip of the rotating object. By replacing v with ωr for my kinetic energy, I am now saying that the transitional energy is dependent on the speed at the tip of the sphere!
Dazed and Confused