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Nathanael
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Yes but do you know an expression for the work done by a spring being compressed?J-dizzal said:48160J +17200x = Wspring
Yes but do you know an expression for the work done by a spring being compressed?J-dizzal said:48160J +17200x = Wspring
.5kx2Nathanael said:Yes but do you know an expression for the work done by a spring being compressed?
Well yes, it's a quadratic equation. You need to use the quadratic formula.J-dizzal said:.5kx2
but when i put them together i get .3211 = x(x-17200) can't go any further.
im getting -8534 and -8665.6 using the quardratic eq. i forgot completing the squaresNathanael said:Well yes, it's a quadratic equation. You need to use the quadratic formula.
(The trick to solving these equations is called "completing the square," but if you "complete the square" for the general expression ax2+bx+c=0 then you will arrive at the quadratic equation, so you can just use that.)
Double check yourself, I get 0.6269mJ-dizzal said:im getting -8534 and -8665.6 using the quardratic eq. i forgot completing the squares
The work done by the spring is equal to the work done by gravity minus work done by friction. This comes from the work-energy theorem which says the change in kinetic energy (in this case zero) is equal to the net work done.J-dizzal said:My homework is past due (midnight). i really need to understand this though.
Nathanael said:The work done by the spring is equal to the work done by gravity minus work done by friction. This comes from the work-energy theorem which says the change in kinetic energy (in this case zero) is equal to the net work done.
The work done by the spring is 0.5kx2
The work done by gravity is mgD (where D is the distance fallen)
The work done by friction is FfD (where D is the distance fallen)
So the equation is 0.5kx2=(mg-Ff)D
The important thing to realize is that D=(2.8+x)
Your mistake was to say D=2.8
It should be 0=150,000x2-17,200x-48,160J-dizzal said:Ok thanks, yea I am having trouble tonight.
my eq is 0=x2 -17200x - 0.3211 does this look right? i keep getting huge values for x.
ok i see now. I am so out of it i can't even do algebra lol. so then part c would be 48160-17200(.6269) J is the energy of the spring pushing and then subtract 48160+friction?Nathanael said:It should be 0=150,000x2-17,200x-48,160
I assume you got your equation by dividing by 150,000? But you forgot to divide the 17200 by 150000.
It should be a plus sign not a minus. Or you could use 150000(0.6269)^2J-dizzal said:48160-17200(.6269) J is the energy of the spring pushing
Ok thanks for all the help again Nathanael. I'll have a new series of problems tomorrow but hopefully will have time to get back at this problem.Nathanael said:It should be a plus sign not a minus. Or you could use 150000(0.6269)^2
For this part you are going to have a change in spring energy, a change in gravitational energy, and the total change in energy will be the work done by friction. The kinetic energy will be zero again.
Maybe you should get some sleep before doing this part
Think about part D as well, that part is more interesting. It will be more satisfying to figure it out yourself so give it some time before asking questions.
Hopefully Nathanael will be well rested to prepare for this.J-dizzal said:Ok thanks for all the help again Nathanael. I'll have a new series of problems tomorrow but hopefully will have time to get back at this problem.