How to find the velocity of a pendulum

[grr_physics]

How to find the velocity of a pendulum...need help!

Homework Statement

A 3.60 m long pendulum with a 1.25 kg bob is pulled sideways until it is displaced 1.80 m horizontally from its rest position. If the bob is released, calculate the speed of the bob when it is 0.250 m about it's rest position.

Homework Equations

I found the potential energy when it passes through rest position= 5.91 J
and the velocity when it passes through rest position is 3.08 m/s. I don't know how to find it at 0.250 m & need help please!

 

[grr_physics]

Need help to find the velocity of a pendulum at a distance please!

1. Homework Statement
A 3.60 m long pendulum with a 1.25 kg bob is pulled sideways until it is displaced 1.80 m horizontally from its rest position. If the bob is released, calculate the speed of the bob when it is 0.250 m about it's rest position.


2. Homework Equations

I found the potential energy when it passes through rest position= 5.91 J
and the velocity when it passes through rest position is 3.08 m/s. I don't know how to find it at 0.250 m & need help please!

 

[Dadface]

I think you mean you found the kinetic energy when it passes through the rest position this being equal to the loss of potential energy.Use the same method,find the vertical distance moved when the horizontal displacement goes from 1.8m to 0.25m and use PE lost=KE gained.

 

[tiny-tim]

Welcome to PF!

Hi grr_physics! Welcome to PF!

I found the potential energy when it passes through rest position= 5.91 J and the velocity when it passes through rest position is 3.08 m/s.

You don't need to do that …

just use conservation of energy (and a bit of elementary trig). ​

 

[grr_physics]

so do i do this:

Ep = Ek
mgh = 1/2mv^2
gh = 1/2v^2
(9.81)(0.250)=1/2v^2

and keep going til i get the answer? where do i do trig?

 

[grr_physics]

so do i do this:

Ep = Ek
mgh = 1/2mv^2
gh = 1/2v^2
(9.81)(0.250)=1/2v^2

and keep going til i get the answer?

 

[tiny-tim]

That's right.

And you'll need the trig to find the height when the horizontal displacement is 1.80 m

 

[grr_physics]

thanks! :)

 

[berkeman]

1. Homework Statement
A 3.60 m long pendulum with a 1.25 kg bob is pulled sideways until it is displaced 1.80 m horizontally from its rest position. If the bob is released, calculate the speed of the bob when it is 0.250 m about it's rest position.


2. Homework Equations

I found the potential energy when it passes through rest position= 5.91 J
and the velocity when it passes through rest position is 3.08 m/s. I don't know how to find it at 0.250 m & need help please!

Two threads merged into one. Please do not multiple post your questions, grr.

 

[grr_physics]

sorry, promise i won't anymore!