HELP - Energy of a rolling sphere (no radius?)

[BlueSkyy]

HELP - Energy of a rolling sphere (no radius??)

Homework Statement

A solid sphere of mass 0.602 kg rolls without slipping along a horizontal surface with a translational speed of 5.18 m/s. It comes to an incline that makes an angle of 34degrees with the horizontal surface. Neglecting energy losses due to friction,

(a) what is the total energy of the rolling sphere?
(b) to what vertical height above the horizontal surface does the sphere rise on the incline?

Homework Equations

KE = 1/2 m (v^2) + 1/2 I (w^2) where I = 2/5 m (r^2)
PE = mgh

The Attempt at a Solution

I'm not given a radius so I can't use the KE equation...where do I go from here?
Once I have a radius it will be much easier to solve the problem...

 

[Doc Al]

Just call the radius "R" and keep going.

 

[BlueSkyy]

i kept "r" as a variable and came up with:
8.0766 + 0.1204 (r^2) (w^2)

but the problem asks for a specific number ( _____ J) so I can't keep the variable "r" there...

also, when they say total energy, do they mean total KE, since the ball is still in motion? I'm trying to use PE to solve for the height once I have KE solved...

 

[Doc Al]

i kept "r" as a variable and came up with:
8.0766 + 0.1204 (r^2) (w^2)

but the problem asks for a specific number ( _____ J) so I can't keep the variable "r" there...

When a sphere rolls without slipping, what's the relationship between the translational speed (v) and the angular speed (w)? (Express the full KE in terms of v and you won't see an "r".)

also, when they say total energy, do they mean total KE, since the ball is still in motion? I'm trying to use PE to solve for the height once I have KE solved...

Total energy means include everything: translational KE, rotational KE, and PE. (When it's on the horizontal surface, I would just call that level PE = 0.)

 

[BlueSkyy]

AH! I forgot!

KE(rotational) = B 1/2 m (v^2) where B = 2/5

Thank you, I figured it out now~
:)

 

[Whome]

E initial = E final
K initial translational + K initial rotational + PE initial = Same except final
is this what you mean? then solve for h on the final side?

 

[Doc Al]

E initial = E final
K initial translational + K initial rotational + PE initial = Same except final
is this what you mean? then solve for h on the final side?

That's right.

 

[Whome]

Thank you.