# A Curious question About Ballistic Pendulum Solution

1. Jan 18, 2015

### terryds

I've watched a video about ballistic pendulum problems.
The illustration is :

I wonder why the final energy is just a gravity potential energy.
I think there is also a rotational kinetic energy (since it will rotate and oscillate)
Is my thought wrong?

2. Jan 18, 2015

### Bystander

What's the rotational velocity at the "peak" of the pendulum displacement?

3. Jan 18, 2015

### terryds

I'm not quite sure. But, I think it will be v/r
Am I right ?

4. Jan 18, 2015

### Bystander

In your sketch, where the maximum displacement from the vertical is indicated to be sixty degrees, how fast is the pendulum moving?

5. Jan 18, 2015

### terryds

Do you mean the velocity ?
I think it's 0 m/s since it has reached the amplitude.
Oh yeah.. Thank you for your answer.
I get it now.. Because the velocity is zero, so the rotational kinetic energy is zero !