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

Final Frequency and Kinetic energy change?

  • #1
17
0

Homework Statement


Hi I know my picture has 2 problems, but lets just focus on the first problem parts a and b.
So for part a it ask for the final frequency after the ant landed, and part b is the kinetic energy difference. Basically the
ant=.01kg, diameter of cylinder is .115m,
the weight of cylinder is .03kg,
and its rotating at 300 rev/min.

Homework Equations


[/B]
deltaK=Kfinal-Kinital
kfinal=.5*i*w where i is the inertia
i=.5*m*r^2
w=w0+at

The Attempt at a Solution


For part a I used the the rotational equation formulas, Im not sire if i picked the correct one though. For part b, its based on part a, basically find the kinital and final with the mass changing from .030g t0 .040 cause the ant has its own weight. Part b I understand its jsut part a I am dont really know where to start?
 

Attachments

Answers and Replies

  • #2
Simon Bridge
Science Advisor
Homework Helper
17,847
1,644
The pic is about a bullet hitting a wooden block.
Note: do not do physics by trying to guess the right formula. Instead, try to figure out what physical principle is at work ... i.e. some sort of conservation law.
Guessing you have a rotating cylinder that an ant drops on ... part b is easier.
Part (a) the frequency will be related to the angular velocity, which is related to both angular momentum and kinetic energy. The kinetic energy is also related to angular momentum.
 
  • Like
Likes CWatters
  • #3
17
0
Omg sorry I uploaded the wrong picture, its this one. Please disreguard the image in my first post. Also for #1 part a, I need to get the final rev/min after the ant falls on it, so I am thinking, w=2*pi*f. But I have two unknowns because I don't know how to get f? unless w= winitial which is 300 rev/min?
 

Attachments

Last edited:
  • #4
17
0
Sorry for double posting but I can't really find Ffinal because I don't see how I can use the initial frequency of 300 to get the final frequency?
 
  • #5
CWatters
Science Advisor
Homework Helper
Gold Member
10,529
2,295
Read Simon's post again. Don't start with equations, think about principles. See if you can reply to this without mentioning a single equation :-) If you get that right, then you can think about which equations might be relevant.

So which principle should you apply here?
 
  • Like
Likes Simon Bridge

Related Threads on Final Frequency and Kinetic energy change?

Replies
3
Views
7K
Replies
5
Views
3K
  • Last Post
Replies
1
Views
628
Replies
2
Views
2K
Replies
5
Views
2K
Replies
2
Views
14K
Replies
6
Views
13K
Replies
2
Views
759
Top