# Physics circular motion and gravity help please

1. Jun 8, 2013

### katiegerster

physics circular motion and gravity help please :(

1. The problem statement, all variables and given/known data

1. a) A solid homogeneous sphere of mass M = 4.80 kg is released from rest at the top of an incline of height H=1.35 m and rolls without slipping to the bottom. The ramp is at an angle of θ = 25.7o to the horizontal. Calculate the speed of the sphere's CM at the bottom of the incline.

b) Determine the rotational kinetic energy of the sphere at the bottom of the incline.

2. Relevant equations

KE= 1/2mv^2
speed= total distance/delta(t)

3. The attempt at a solution

not sure how to go about solving this..

2. Jun 8, 2013

### voko

What about rotational kinetic energy? Don't you have an equation for that?

3. Jun 8, 2013

### katiegerster

oh KEr= 1/2(I)(w^2)

4. Jun 8, 2013

### voko

So the ball starts at some height and rolls down. Can you use conservation of total energy?

5. Jun 8, 2013

### katiegerster

i wasnt sure if i could use that or not

6. Jun 8, 2013

### voko

What are the conditions for its applicability?

7. Jun 8, 2013

### katiegerster

i dont know what you mean,
but if i could use the conservation of energy this is the formula i have
(1/2mv^2+1/2Iw^2+mgh)i= (1/2mv^2+1/2Iw^2+mgh)f

8. Jun 8, 2013

### voko

Let's put it this way: is there any reason you know of you cannot use this formula? If no, what prevents you from using it?