hey Matt, this has been very helpful. I think the smart glass works for me. also, it's very cool when the students participate. cheers.

Thank you for explaining this so well! Glad to have you as a teacher.

@yoprofmatt

4 жыл бұрын

exhilir, You're very welcome. Glad you're enjoying the videos. You might also like my new site: www.universityphysics.education Cheers, Dr. A

This is very detailed and understandable, musch respect for you prof

@yoprofmatt

3 жыл бұрын

Shovel Nyan, Much appreciated. Thanks for the comment, and keep up with the physics! You might also like my new website: www.universityphysics.education Cheers, Dr. A

BEST PHYSICS LECTURES EVER !!!

Great video! 👍

thank u very much this was very helpful

The string has a horizontal force working on the bullet during the swing. I think that’s why horizontal momentum is not conserved. I hope I understand it correctly.

the best tutor ever........ much respect........

@yoprofmatt

6 жыл бұрын

Thank you. I'm glad to hear you're finding these useful. Keep up with the physics. Cheers, Dr. A

Thank you doctor strange.

Things make so much more sense years later...

Aww this is great, I love this problem. So, okay; lets say that instead of pendulum, the bullet hits a block attached to a spring. We can use the same set up by replacing mgh with 1/2 kx^2 (spring potential energy) while the external force causing the loss of momentum is the frictional force, right? *finger's crossed*

@yoprofmatt

5 жыл бұрын

Jossy, Correct, mostly. Momentum is conserved when the bullet digs into the block. The bullet stops due to friction between the wood and the bullet. Of course, mechanical energy is not conserved here (you put a big pit into the wood and this took energy), but momentum is conserved. Now the block is moving and starts to compress the spring. At this point you conserve energy, so the kinetic energy of the block turns into potential energy of the spring once it's completely compressed. For this part, assume no friction. So you are correct that you can replace mgh with 1/2 kx^2 and you'll get the right answer, but I wanted to comment on your language. Cheers, Dr. A p.s. You may uncross your fingers now.

When the bullet enters the block would it be a perfectly inelastic collision not an inelastic collision?

@yoprofmatt

6 жыл бұрын

Bullet entering block is certainly an "inelastic" collision because it has to push wood fibers out of the way, which takes energy. Cheers, Dr. A

An easier way would be to set the initial kinetic energy of the bullet itself equal to the final gravitational potential energy of the bullet + block.

@Munneh

5 жыл бұрын

I don't know about this, as I believe some energy from the bullet will be converted to sound and heat, so therefore it wouldn't completely be conservation law of energy. That is why DR. A split it into two parts because the initial part where the bullet and block are separate will cause an inelastic collision, so momentum should instead be used. But I might be wrong.

how does he write backwards so well

@yoprofmatt

6 жыл бұрын

He doesn't. He cheats. Answer here: www.learning.glass Cheers, Dr. A

Why does energy conserves?

Do you write backwards???????

Thank-you sir for very nice explanation Student of India😂😂

What I'm wondering is, why doesn't he solve for V1 just using the momentum equation directly instead of solving for V2 ?? (Someone please answer)

@jeffreyl2403

6 жыл бұрын

Kinetic energy is not conserved during the inelastic collision because mechanical energy is lost when the bullet penetrates the wood. momentum is not conserved during the blocks movement upward because the force of gravity is acting on it. So the velocity of the bullet cannot be directly determined through by equating these end points. We instead use the point after impact because once the collision has ended the kinetic energy of the system is conserved. Once we know the velocity of that block, we can use the conservation of momentum to find the velocity of the bullet because momentum is conserved during the collision. I too am learning

@seara5762

6 жыл бұрын

well, if you set the first set of equations to solve for V1, then you don't have enough information to solve for V1. V2 would be an unknown value. However if you go the other way around like what he did, through second set of equations (E conserved), you have another equation for V2 which you could plug in the values and solve for V1. I mean hopefully I was answering your question. This is what I thought. Im learning here too :)

@JossinJax

5 жыл бұрын

Searam Park is correct. It all depends on what you're given to start off with. With the first equation, you can solve for either V1 or V2, and likewise plugin for whichever you're trying to solve for in the second equation. In this example, he chose to solve for the initial velocity of the bullet, very much like most homework and test questions will ask for and hence "ballistic".

What if the Block was not selected, the engineer or physicist did not run the numbers and select the proper length, thickness, hardness, mass of the wood engineered to match the parameters of the velocity and mass of the bullet to absorb it, and it just disintegrates? Lol...

@yoprofmatt

2 жыл бұрын

I think then it's tough to do the same measurement. Cheers, Dr. A

Can anyone help me on this experiment? Attach contact info

are you happy that you spent 3.3k on a piece of glass

Are you writing backwards?

@yoprofmatt

2 жыл бұрын

Nope. Mirror image of the writing. Cheers, Dr. A

Am I the only one blown away by how he is able to write everything backwards so easily??

@yoprofmatt

2 жыл бұрын

No, but sadly not true either. See: kzread.info/dash/bejne/dYt8r9aMfq7eiaQ.html Cheers, Dr. A

the squeaking of the marker is horrible

@yoprofmatt

4 жыл бұрын

Christine, Agreed. We are fixing it on my new website: www.universityphysics.education Cheers, Dr. A