ME 274: Dynamics: Chapter 14.5 - 14.6

[@dieguinf1988]

You save lives! Thanks for the videos!

[@ColinSelleck]

Diego Mosquera You are welcome.

[@JesseTheAceReal]

Your videos make a lot more sense to me than my own teachers lectures. thanks a bunch for being so descriptive.

[@ColinSelleck]

You're welcome!

[@rabbi_art]

This guy is THEE GUY, thank you 👊

[@ColinSelleck]

Thanks!

[@mohamedBakey]

First of all thank you very much for your great work i have a question how do i know if I should use T1+V1=T2+V2 or that i should use T1+U1-2=T2

[@ColinSelleck]

Use the first equation (cons. of energy) when only conservative forces are involved (gravity and springs). Conservative forces are those whose potential energy is independent of the path taken. Use the other (work and energy) when there is friction or external forces acting on the particle/body.

[@EngAhmadAnan90]

really thank you sooooo much ..... words cant save me to thank u .... but i have Q. depends on @mohamed Q. ..... how could i use that 2 equations together? do u have problem contain them ??

[@ColinSelleck]

Since the first equation is a special case of the second equation, (i.e., the absence of non-conservative forces), it is not wise to combine them. Each represents a method for solving a problem (i.e., cons. of energy & work/energy) .

[@EngAhmadAnan90]

Colin Selleck THANK YOU 😊

[@aksharpatel7111]

Hi Prof. Selleck, first of all thank you so much for uploading these wonderful lecture videos. They are really helpful. I had a question though; at 6:32 mark, the potential spring energy at point A was written as Va = (1/2)*(400)*(0.1)^2. Won't that be Va = (1/2)*(400)*((0.2)^2 - (0.1)^2)? And same thing for Potential spring energy at point B. I am not sure if I am right but I am really confused as to whether it is (s2-s1)^2 or ((s2)^2 - (s1)^2).

[@ColinSelleck]

When computing the potential energy of a spring at a point, you use (1/2)ks^2. If you want the difference in potential energy between two points, you use (1/2)k(s2^2 - s1^2). Never use (1/2)k(s2-s1)^2. In this case, I am computing the potential energy of the spring at a point so I use (1/2)ks^2. Remember that s is always measured from the unstretched spring length, so it is the distance the spring is compressed or stretched.

[@aksharpatel7111]

Colin Selleck Thank you sir, that made things a lot more clear

[@makkam999]

Sir, at 6:36 how did you compute that length of .3 the vertical that you used for potential and also the .5 you used for the second spring force. im a visual learner and im not really seeing how you go that. Thank you

[@ColinSelleck]

Call the point where the spring is attached point C. The distance between C and A is 0.1 m (see the figure). The unstretched length of the spring was given as 0.2 m. So the spring is compressed (0.2 - 0.1) m at point A. The distance between C and B is 0.5 m (see the figure). So the spring is stretched (0.5 - 0.2) m at point B.

[@shengfenglee97]

why can't find Vc by relating to position b??

[@ColinSelleck]

You can use the energy equation between points B and C: 1/2(800)(8.578^2) = 1/2(800)Vc^2) - 800(9.81)(20). Vc = 21.6 m/s.

[@masonthao835]

Need instructor like you in my school. thanks alot.

[@ColinSelleck]

You're welcome!

[@wadzanaichikuhuhu8896]

good job....this was really helpful

[@ColinSelleck]

Thanks!

[@abelalfeuz5860]

why the sign for mg is not negative...can u explain?

[@ColinSelleck]

What time stamp are you referring to?

[@jalalidrees3648]

Sir i have a question how you come up with 0.5m and 0.3 mean from where you find this because in question it is not given ??

[@ColinSelleck]

The 0.3 comes from 0.4 (radius) - 0.1 (vertical drop from A to C). The 0.5 comes from Pythagorean Theorem: sqrt(0.4^2 + 0.3^2) .

[@jalalidrees3648]

Thanks sir

[@ColinSelleck]

@@jalalidrees3648 You're welcome.

[@abdulmynaem]

Thanks!

[@ColinSelleck]

+Abdulmunaem Al-lwati Glad they are helping you.

[@jjjjjjjjjjjoeskatess]

Doing god's work.

[@ColinSelleck]

Glad to help.

[@Kvele]

I was watching this video but stopped halfway through. If I had watched all the way through I would have seen the last problem which was on my exam that I was studying for lol.

[@ColinSelleck]

Ha!

[@kasemfakhro5524]

sooooo helpful

[@ColinSelleck]

+Kasem Fakhro Thanks for letting me know.