Conservation of Mechanical Energy

Click For Summary

Homework Help Overview

The problem involves the conservation of mechanical energy in a system where a block is hanging from a string wrapped around a solid cylinder. The block falls a specific distance over a set time, and the original poster seeks to calculate the mass using energy principles.

Discussion Character

  • Exploratory, Assumption checking, Mathematical reasoning

Approaches and Questions Raised

  • Participants discuss the application of conservation of energy principles and the relationship between potential and kinetic energy. There is a focus on clarifying the meaning of variables such as R and r in the equations presented.

Discussion Status

Some participants have pointed out potential errors in calculations and clarified the significance of certain variables. There is an ongoing exploration of how to approach the problem without needing to know the radius explicitly, as it may cancel out in the equations.

Contextual Notes

The original poster expresses uncertainty about finding the radius and how it factors into the energy equations, indicating a need for clarification on the setup and assumptions of the problem.

Lma12684
Messages
24
Reaction score
0

Homework Statement


A massless string is wrapped around a solid cylinder as shown in the diagram. A block of mass 2kg hangs from a string. When released, the block falls a distance of 82 cm in 2.0 seconds. Calculate the mass using the conservation of mechanical energy.


Homework Equations


d=speed(i) + 1/2at^2
a=.205 m/s

V(f)=v(i) + at
v(f)=.41 m/s^2

PE=KE(block) + KE(cylinder)
mgy=1/2mv^2 + 1/2(1/2MR^2)(v/r)^2


The problem is that I do not know how to find R? Please help!










The Attempt at a Solution

 
Physics news on Phys.org
Hi Lma12684,

I think you neglected the 1/2 in your equation when you calculated a.

For the value of R, what do R and r represent in your final equation?
 
My apologies, they represent the radius. I didn't mean to use different symbols.
 
So you can see now why you do not need to know the radius?
 
Because they cancel??
 
That looks right; once you correct a and vf I think you can solve the energy equation.
 
Thank You~!
 

Similar threads

  • · Replies 9 ·
Replies
9
Views
1K
  • · Replies 37 ·
2
Replies
37
Views
2K
Replies
2
Views
2K
Replies
1
Views
1K
Replies
2
Views
1K
  • · Replies 5 ·
Replies
5
Views
978
Replies
28
Views
2K
  • · Replies 8 ·
Replies
8
Views
2K
Replies
4
Views
1K
  • · Replies 12 ·
Replies
12
Views
3K