What are the Maximum Speeds of a Pendulum with Attached Mass?

  • Thread starter Thread starter SherlockOhms
  • Start date Start date
  • Tags Tags
    Mass Pendulum
Click For Summary

Homework Help Overview

The problem involves a pendulum with a mass that reaches a certain height, and the task is to calculate the maximum speeds in both the x and y directions given specific parameters. The context is rooted in mechanics, particularly focusing on energy conservation principles.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning

Approaches and Questions Raised

  • The original poster attempts to apply conservation of energy to find the maximum speeds, questioning how to approach the calculation for the y-component of velocity. Some participants suggest deriving expressions for potential energy and velocity as functions of the angle θ, while others clarify the role of θ in the context of the pendulum's motion.

Discussion Status

Participants are engaging in a productive dialogue, exploring the relationship between potential energy and the angle of the pendulum. There is a recognition of the need to clarify the variable θ and its relevance to the calculations, with some guidance provided on how to express energy in terms of θ.

Contextual Notes

The original poster notes a lack of information regarding the angle θ, which is central to the discussion. There is also an acknowledgment that the angle changes over time, leading to further questions about its initial value and necessity in solving the problem.

SherlockOhms
Messages
309
Reaction score
0

Homework Statement


A pendulum of mass "m" reaches a height "h" , while the length of the pendulum is R. If the R = 262 cm and h = 136 cm: (a) calculate the max speed in the x-direction.
(b) calculate the max speed in the y direction.


Homework Equations


K = 1/2(m)(v)^2.
U = mgh.
Vector components.

The Attempt at a Solution


Calculating the max speed in the x direction is grand, it obtains a maximum value at the bottom of the arc so using conservation of energy you can calculate it to be v = sqrt(2gh). This is due to the vector components of the pendulum's velocity being v = vcos(θ)x + vsin(θ)y. The x-component obtains a max value when cos(θ) = 1 which occurs at θ = 0 (i.e. the bottom of the arc). Wouldn't the y-component then obtain a max value when θ = pi/2? This angle is never actually reached due to the bob only being raised through a height "h".
So calculating the max velocity in the y is a little trickier. Could somebody give me some advice on what to do next? I'll attach a picture of the diagram.
 
Physics news on Phys.org
ImageUploadedByPhysics Forums1366399180.541798.jpg
 
You should be able to write down an expression for the potential energy of the mass as a function of ##\theta##. Using it, you can derive an expression for v as a function of ##\theta##.
 
vela said:
You should be able to write down an expression for the potential energy of the mass as a function of ##\theta##. Using it, you can derive an expression for v as a function of ##\theta##.

I'm not given θ though. Is there enough information given to find it?
 
##\theta## is a variable that tells you where the pendulum is. It changes with time. Did you mean ##\theta_0##, the initial value of ##\theta##? You are, in fact, given enough information to find it, but I'm not sure why you'd need it.
 
Ok, ok. I see what you're saying now. Misunderstood your first reply. Thanks!
 

Similar threads

  • · Replies 26 ·
Replies
26
Views
4K
  • · Replies 5 ·
Replies
5
Views
2K
  • · Replies 9 ·
Replies
9
Views
3K
Replies
1
Views
1K
Replies
3
Views
1K
  • · Replies 4 ·
Replies
4
Views
2K
  • · Replies 1 ·
Replies
1
Views
1K
  • · Replies 3 ·
Replies
3
Views
3K
  • · Replies 38 ·
2
Replies
38
Views
4K
  • · Replies 5 ·
Replies
5
Views
6K