Im stuck: Energy in rotational motion

[Edwardo_Elric]

Homework Statement

A uniform rope 12.0m long and with a mass 3.00kg is hanging with one end attached to a gymnasium ceiling and the other end just touching the floor. The upper end of the rope is released, and the rope falls to the floor. What is the change in the gravitational potential energy if the rope ends up flat on the floor(not coiled up) ?

Homework Equations

Fx = 0
Fy = 0
U = mgh1 - mgh2

The Attempt at a Solution

Fy = 0 = Tsin(theta) - W
Tsin(theta) = W
T = ((3(9.8))/(sin(theta))

Fx = 0 = Tcos(theta)
No other force acts on the x-axis

 

[learningphysics]

change in gravitational potential energy = mgh2 - mgh1

that's all you need.

 

[Edwardo_Elric]

I thought it was inclined


U = mgh2 - 0
= (3.00kg)(9.8m/s^2)(12.0m)
= 352.8 J

thankss

 

[learningphysics]

I thought it was inclined


U = mgh2 - 0
= (3.00kg)(9.8m/s^2)(12.0m)
= 352.8 J

thankss

wait. use the center of mass... what's the height of the center of mass? you need to use 6.0m not 12.0m.