# Homework Help: Spherical motion stuff

1. Mar 12, 2006

### alex_boothby

would

(5/7) gsinΘ (the symbol is a theta)

give me the average acceleration of a solid sphere rolling down an incline, im not also sure where the 5/7 came from, ive herd of 2/5 for inertia but... AND is that linear acceleration or rotational.

i also get about 0.6 when i calculate the acceleration from my data by 2s/t^2 which is from s=ut+ 1/2 at^2

im also confused to why when i do v(final) - v (intial) / time
i do not get 0.6 well i do for the first value, then for the other distance i do not!!!!!
and ages ago i got 0.3 but now i cant even remember were that came from, i do get 0.3 if i do that eqaution for average v, but once again only for the first value.

thanks for any help, i think i just need reasuring that i am doing it right, as i have got .6 from to different things.

2. Mar 12, 2006

### vaishakh

Under no friction condition the particle will simply slide. You have mentioned nothing about friction here.

3. Mar 12, 2006

### alex_boothby

thats hasnt yet come into it yet, i want to verify that the above calculations are correct first

4. Mar 12, 2006

### vaishakh

Sorry - its given to be rolling in the question.
Well the force on the body is mgsin(theta) and that should be the acceleration.

5. Mar 12, 2006

### Staff: Mentor

Don't just use some equation at random that you plucked from a book. Especially if you don't know know what it's supposed to be for.

That equation is correct (for a solid sphere rolling without slipping down a flat incline), but derive it yourself using Newton's 2nd law if you plan on using it. (You should be able to tell whether it's linear or angular acceleration by just looking at the units.)

6. Mar 12, 2006

### alex_boothby

well thers no inertia so i assume its linear, i tried to derive it from newton second law, but got awfuly baffeled and decided long as it works nicely!!