• Support PF! Buy your school textbooks, materials and every day products Here!

Rotational Motion of a marble

  • Thread starter valeriex0x
  • Start date
  • #1
43
0

Homework Statement



A solid uniform marble and a block of ice, each with the same mass, start from rest at the same height H above the bottom of a hill and move down it. The marble rolls without slipping, but the ice slides without friction.

Find the speed of each of these objects when it reaches the bottom of the hill.
Vice:?
Vmarble:?

Homework Equations



1/m v^2 = mgh

The Attempt at a Solution



Ice:
1/2 mv^2=mgh

v= squareroot 2gh

Marble:
mgh=1/2 mv^2 + 1/2 I ω^2

=1/2 mv^2 +1/2(2/5 mr^2) (v/r)^2

The answers i entered in were marked incorrect by masteringphysics.

Please advise!!!!!!!! : (
 

Answers and Replies

  • #2
I like Serena
Homework Helper
6,577
176
Hi valerie! x0x :smile:

Your v for the block of ice is correct.
And your equation for the marble is correct too.

The only thing missing is that you didn't give v of the marble.
Did you solve your equation for v?
 
  • #3
43
0
well i got stuck.... and i dont know why its marking me wrong. for the marble i got v: squareroot 2/4 mgh


anythoughts?
 
  • #4
I like Serena
Homework Helper
6,577
176
well i got stuck.... and i dont know why its marking me wrong. for the marble i got v: squareroot 2/4 mgh


anythoughts?
I'm afraid that in that case you did not solve your own equation correctly.

For starters, there should not be an "m" in there.
There isn't an "m" for the block of ice either!

But your fraction of 2/4 is wrong too.

How did you arrive at your solution for v?
Can you show some (major) steps?
 
  • #5
43
0
oh never mind .......... this stupid mastering physics wanted a capital H instead of h.

aughhhhhh!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! the marble was squareroot 10 gh/7
 
  • #6
43
0
thanks for your help!!!!!! i caught that at the last min!
 
  • #7
I like Serena
Homework Helper
6,577
176
Congrats with your right answer! :smile:
 

Related Threads on Rotational Motion of a marble

  • Last Post
Replies
6
Views
2K
  • Last Post
Replies
6
Views
4K
  • Last Post
Replies
4
Views
2K
  • Last Post
Replies
13
Views
4K
Replies
2
Views
1K
  • Last Post
Replies
1
Views
5K
Replies
9
Views
822
  • Last Post
Replies
0
Views
876
  • Last Post
Replies
2
Views
3K
Top