Ball launcher question - ENERGY

[ahsila432]

Homework Statement

So, we've been shown a video in which a ball in launched and we were required to make sketches with all the data given in this video (launch height, ball mass etc.) Then we were asked to determine which ball lost more energy. I completed my mathematical solution but my teacher said "Good up to this point, however this one step remaining". I've been trying to figure it out for superrr long but I'm not sure. Ive attached the sketch of what is going on so you have all the data.

Relevant Equations

Energy equations

I got 12/12 on the above part^

And as for the mathematical solution below I got 5/6 and then 2.5/3 for the conclusion.

 

[ahsila432]

I would like to know what the last remaining step is or if there's another way to find the answer maybe.

 

[PeroK]

I'm not sure what you're actually trying to calculate here.

 

[ahsila432]

Two balls were shown (a large and small ball) and the question is " Which one of the two loses more energy" due to friction as it is pulled back on the launcher. I calculated the work of friction done, above my conclusion statemment you can see, our teacher said that "you can't directly calculate the energy loss"

 

[PeroK]

How is friction relevant on a launcher?

 

[ahsila432]

This is the video:
I think when he pulls back there is friction from the wood and ball

 

[PeroK]

I don't see the relevance of friction as a cause of energy loss.

 

[ahsila432]

maybe in the initial elastic energy? I am not sure, this is just what my teacher asked

 

[PeroK]

maybe in the initial elastic energy? I am not sure, this is just what my teacher asked

I would also question why you think the larger ball loses more energy?

 

[ahsila432]

I calculated Wf and it seemed to be bigger for the larger ball (in my mathematical solution in the image). But I don't know if that's the right answer.

 

[PeroK]

I calculated Wf and it seemed to be bigger for the larger ball (in my mathematical solution in the image). But I don't know if that's the right answer.

What's $W_f$?

I would have assumed this assigment related to elastic PE, kinetic energy and gravitational PE.

 

[ahsila432]

Wf is the work of friction and yes, there is kinetic energy and gravitational energy, I included those in the LOL diagram and my equation

 

[PeroK]

Wf is the work of friction and yes, there is kinetic energy and gravitational energy, I included those in the LOL diagram and my equation

Okay, let's go back to my question:

I would also question why you think the larger ball loses more energy?

I don't understand why you reached that conclusion.

And, I'm fairly sure friction is not the answer in any case!

 

[ahsila432]

he said my answer was good up to the second step, I just need to add one more thing and he told us to consider the friction

 

[haruspex]

I don't understand the question "which ball?" There is only one ball in the video, shown once at normal speed and once in slow motion.
Even if they are separate launches, they appear to reach the same height.
Is there a second video, or does the question relate to a lab exercise based on the video?

Neither is it clear what phase is being considered for energy loss, nor how the masses compare. I'll assume the balls have the density, so larger is more massive.
Energy could be lost at two stages:
1. Transfer of energy from spring to ball. The lighter the ball, the greater the launch speed, so the greater the energy left as KE of the launcher. OTOH, a more massive ball would increase the normal force on the spring's pivot, so more friction.
2. Drag during ascent. What affects the energy loss to drag?

 

[ahsila432]

The video is a different one that shows the same thing but with two different balls (a big ball and a small ball) and the question is which of the two balls loses more initial elastic energy. And we have to determine this mathematically using energy equations.

 

[ahsila432]

The masses are given in the physics sketch too one ball is 0.0285 kg and the other is 0.067 kg

 

[haruspex]

The video is a different one that shows the same thing but with two different balls (a big ball and a small ball) and the question is which of the two balls loses more initial elastic energy. And we have to determine this mathematically using energy equations.

Ok, thanks for the clarification.

due to friction as it is pulled back on the launcher.

I don't see that any friction as the launcher is pulled back can be relevant.
But you still have not clarified whether you are concerned with the launch phase only, the ascent of the ball, or both.

 

[ahsila432]

launch phase

 

[haruspex]

launch phase

Then I refer you to bullet point 1 in my post #15.

 

[ahsila432]

Thanks! Could I get the link to that post, I am new to the website so I'm not sure how to find it

 

[hmmm27]

Thanks! Could I get the link to that post, I am new to the website so I'm not sure how to find it

haruspex was referring to post #15 in this thread. You can find the post number at the top of the post, on the blue bar, on the right hand side. This post is #22.