Problem F14-5 Dynamics Hibbeler 13th (Chapter 14) Engineering Dynamics - Work and Energy

[@kevincamarillo2429]

the algebra doesnt make sense for teh quadratic equation s^2: -100 s: 100-49.05 = 50.95 constant: 125-60+36+29.43 = 130.43 tell me if im wrong please

[@3E37]

when i do the simple math i get 100s2+50.95s+130.43 how do you get those numbers the 100s2+ 198.1s-42.14

[@genarorivera9750]

Yeah, I kept getting that hoping someone else pointed it out to assure my answer

[@rickjljr11]

I realize this is old and not much interest, but does anyone have a published answer key for this problem? As a challenge I was trying to solve the ODE d^2x/dt^2 = -k/m*(x-0.6) + 149/m with x0 = 0.6 and v0 = 5. KZbin has 4 videos working this problem with 4 (maybe 6) different answers. After a lot of work I came out with s = 2.6889 but still not sure.

[@johnbach2077]

Huge help, thank you!

[@julianfigueroa5675]

TE AMO SOS LO MEJOR QUE ME HA PASADO

[@theengineeringcrucible3490]

Me alegro que te están ayudando los videos

[@Infynte-k9y]

I thought since the plane the block is sliding is smooth therefore, there is no friction. So then why are we figuring out T_1 if it is supposed to be 0?

[@z4rff145]

T1 no puede ser cero porque ya viene con una velocidad, T2 es 0 porque frena y no existe movimiento, sorry 6 month later

[@jimfoug3061]

I tried solving this using F=ma and net force but for some reason i am getting the wrong answer. Net force (-30degrees)= 100 + sin(30)mg -200s ma = 149.05 - 200s 10v dv = (149.05- 200s)ds then i integrated with v going from 5 to 0 and and s going from .6 to s. My answer was 1.873 meters. Any idea why it was wrong? thank you

[@carterg.3606]

got the same thing using work energy theorem

[@hanzedwardmaningo9055]

Where did you get the 198.15 and 42.14 after you simplyfying?

[@theengineeringcrucible3490]

Yes that was from simplifying the equations in blue towards the bottom :)

[@iskendersefaylmaz4963]

I think your answer is not correct. While calculating the spring energy, the first length should be taken as 0 not 0.6

[@mahmoud47]

hallo thank you for your solution. only I have a comment on Spring's energy because you got it wrong Us=0.5K(s2-0.6)^2 ... Not Us=0.5K((s2)^2-(0.6)^2 ) the sping was unstretched when s=0.6 so x1=0 , then the spring was stretched so that x2=S2-0.6 Thanks again for your great job

[@victorhu7280]

I don't think you are doing it right, because there's no work done in the spring when it's equal to 0.6, it's supposed to be (S2-0.6)square

[@QuintenVandenbergh]

Yes, it's wrong.

[@victorhu7280]

@@QuintenVandenbergh Good, someone else sees it, haha

[@rashidbinmansour8319]

thank you very much u saved me. and Also thanks to The Engineering Crucible for his videos it help me a lot.

[@NielsCoopmans]

the energy from gravity isnt negative

[@theengineeringcrucible3490]

Trying to recall what I was doing, but essentially the work from gravity comes out to be positive. While I wrote it down as negative, the s2-s1 should give you negative result thus cancelling out the negatives.

[@awodiyaphilip6742]

​@theengineeringcrucible3490 but it's still negative since s is positive

[@abdullahelgamal9759]

Its + cos(30) not -sin(30) because its on a decline so when we resolve the wight its going to be to the right and down we need the force to the right cause its gonna push with the force so +10x9.81cos(30)(S-0.6) the rest is correct

[@Shamano37]

Incorrect, gravity acts in the Y direction, so we need to use sin to find the force in the Y.

[@HashemAljifri515]

Your answer is wrong. The correct answer is s= 1.873 + 0.6 = 2.473 meters.

[@rickjljr11]

I agree. I did the problem two ways. If you add F=100 and the force due to gravity, 49.05, the spring at its equilibrium point is X_equil = 1.3453. If you then solve the differential eq with x'(t)=5 you get an amplitude of c2 = 1.1180 which give a max of 2.4633.

[@HashemAljifri515]

@@rickjljr11 Yo good luck in dynamics man I passed 🌝 . And I hope yo do too