- #1

flyingpig

- 2,579

- 1

## Homework Statement

http://www.collegeboard.com/prod_downloads/ap/students/physics/ap04_frq_physics_cm.pdf

Question 2 part c)

"Calculate the rotational inertia of the pulley"

Answer Key: http://www.collegeboard.com/prod_downloads/ap/students/physics/ap04_frq_physics_cm.pdf

## The Attempt at a Solution

Something about the alternative solution makes no sense to me

½m(v² - v₀²) + mg(h - h₀) + ½I(ω² - ω₀²) = 0

½m(v² - 0) + mg(0 - D) + ½I(ω² - 0) = 0

-mgD = -½Iω² - ½mv²

Now here comes the problem the solution said the kinetic energy is the CHANGE for the block, not the pulley, so how come when I is solved, it is assumed that I is for the pulley? Since the energy is calculated for the CHANGE for the block and not the pulley.