Is 51 micro joules the maximum kinetic energy of this pendulum?

  • Thread starter Thread starter Bolter
  • Start date Start date
  • Tags Tags
    Maximum Pendulum
Click For Summary
The discussion revolves around calculating the maximum kinetic energy of a pendulum, with a focus on the given time period and amplitude. The calculated kinetic energy of approximately 50.98 micro joules is considered reasonable, but there are suggestions to clarify the definition of "amplitude" and its impact on the calculation. It is emphasized that using maximum potential energy can serve as a verification method. Additionally, participants note the importance of maintaining consistent significant figures based on the least precise input. Overall, the calculations and definitions are crucial for accurately determining the pendulum's kinetic energy.
Bolter
Messages
262
Reaction score
31
Homework Statement
Calculate the maximum kinetic energy of the pendulum
Relevant Equations
angular speed = 2 pi/T

KE = 1/2mv^2
Screenshot 2020-02-25 at 17.47.25.png

So I have been given a question here which asks me to work out the maximum kinetic energy of the pendulum

It has given info such as time period and amplitude, which I had then made use of these formulas

IMG_3992.JPG


Does a kinetic energy of approx 50.98 micro joules seem right here?

Any help would be great! Thanks a lot
 
Physics news on Phys.org
I think it's okay (I didn't pay very much attention to the numbers). But if you were my student, I would highly recommend you to put always the units so, when computing ##v_{max}##, put
$$v_{max}=2.9 \text{ s}^{-1}\cdot 0.05 \text{m} = 0.14 \text{ms}^{-1}$$ and so on.
 
Bolter said:
Homework Statement:: Calculate the maximum kinetic energy of the pendulum
Relevant Equations:: angular speed = 2 pi/T

KE = 1/2mv^2

View attachment 257680
So I have been given a question here which asks me to work out the maximum kinetic energy of the pendulum

It has given info such as time period and amplitude, which I had then made use of these formulas

View attachment 257681

Does a kinetic energy of approx 50.98 micro joules seem right here?

Any help would be great! Thanks a lot
Looks about right.

You could calculate the answer using maximum potential energy to check it yourself.
 
How is "amplitude" in centimeters defined? Is it the change in elevation, or is it an arc-length? Does the answer (max KE) depend on the gravity field (are we on the Earth or the moon)? I'm trying to figure out if we need those defined, or if period (which gives L/g) is sufficient to answer.
 
Bolter said:
Does a kinetic energy of approx 50.98 micro joules seem right here?
You should not quote more significant figures than in your least precise input, so make it 51.
 
The book claims the answer is that all the magnitudes are the same because "the gravitational force on the penguin is the same". I'm having trouble understanding this. I thought the buoyant force was equal to the weight of the fluid displaced. Weight depends on mass which depends on density. Therefore, due to the differing densities the buoyant force will be different in each case? Is this incorrect?

Similar threads

  • · Replies 27 ·
Replies
27
Views
2K
  • · Replies 9 ·
Replies
9
Views
2K
  • · Replies 31 ·
2
Replies
31
Views
4K
  • · Replies 7 ·
Replies
7
Views
3K
  • · Replies 3 ·
Replies
3
Views
3K
  • · Replies 7 ·
Replies
7
Views
2K
  • · Replies 5 ·
Replies
5
Views
3K
Replies
8
Views
2K
  • · Replies 12 ·
Replies
12
Views
2K
Replies
5
Views
10K