- #1

devanlevin

t?

this is a kinematics question i have for homework and just dont know where to turn to. i tried with the equations but seem to always have something missing

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- #1

devanlevin

t?

this is a kinematics question i have for homework and just dont know where to turn to. i tried with the equations but seem to always have something missing

- #2

Kurdt

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What have you tried? IF you show your work people will be in a better position to help you.

- #3

devanlevin

v(t)=vo+at

x(t)=Xo+Vot+0.5at^2

v^2-Vo^2=2a(delta)X

or other variations of these equations

every time i come up with 1 equation with 2 missing numbers and the i get stuck, for example, using the 1st and saying that at max height Vy0=0, i get stuck because i dont have sin(theta) or T

using the 2nd and saying that Yf=400 i still dont have sin(theta) or T

using the 2nd and saying Xf=15000 dont have cos(thetha) or t

ising the 3rd dont have V unless i say Vy at max height is 0 but then dont have delta Y

- #4

Kurdt

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- #5

devanlevin

please help, i have another 4 questions of this sorty and cant continue my homework till i understand it, my next class is on monday and need to finish the work before it

- #6

Kurdt

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- #7

devanlevin

then i must put that same t into my y equation, but how do i get from cos(theta) to sin(theta)??

do you understand why i cant solve this or am i just being an idiot

- #8

Kurdt

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- #9

tiny-tim

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Hi devanlevin!i did that, i get , for x- t=3.75/cos(theta)

then i must put that same t into my y equation, but how do i get from cos(theta) to sin(theta)??

(Don't you mean 37.5?)

- #10

devanlevin

15000=400xcos(th)xt

t=37.5/cos(th)

cos(th)=37.5/t

for y

400=400xsin(th)xt-4.9t^2

t=81.633sin(th)

sin(th)=0.01225t

now from this how do i find theta??

- #11

Kurdt

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Not sure what all the bold bit is. You want to substitute the t in your y equation for the t you got from the x equation.

15000=400xcos(th)xt

t=37.5/cos(th)

cos(th)=37.5/t

for y

400=400xsin(th)xt-4.9t^2

t=81.633sin(th)

sin(th)=0.01225t

now from this how do i find theta??

- #12

tiny-tim

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Hi devanlevin!

15000=400xcos(th)xt

t=37.5/cos(th)

cos(th)=37.5/t

for y

400=400xsin(th)xt-4.9t^2

t=81.633sin(th)

sin(th)=0.01225t

now from this how do i find theta??

(have a theta: θ

and a squared: ²

oh … and

I don't know how you got the 81.633 either.

Hint: get cosθ and sinθ on the left, then square and add.

- #13

devanlevin

my problem is that if i substitute the t i found from the X, i get an equation with sin(theta) and cos(theta) which i think i can turn into tan(???) but i also get cos^2 from the t^2 and then dont know how to bring them to a result for theta

400=400sin(th)x37.5/cos(th)-4.9x(37.5/cos(th))^2

- #14

Kurdt

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http://en.wikipedia.org/wiki/List_of_trigonometric_identities

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