let the angle be Ø, and the horizontal distance be x
given : dx/dt = 9
find dØ/dt
we have a right angled triangle, and
tanØ =100/x
xtanØ = 100
x sec^2 Ø dØ/dt + tanØ (dx/dt) = 0 ***
when 200 ft are let out,
x^2 + 100^2 = 200^2
x^2 = 300
x = 10√3
secØ = 10√3/100 = √3/10
sec^2 Ø = 3/100
tanØ = 100/10√3 = 10/√3
in ***
(10/√3)(3/100) dØ/dt + (10/√3)(9) = 0
solve for dØ/dt
A kite 100 ft above the ground moves horizontally at a speed of 9 ft/s. At what rate is the angle (in radians) between the string and the horizontal decreasing when 200 ft of string have been let out?
4 answers
sorry I didnt get whats the answer
oh, please -- do some of the work, okay?
(10/√3)(3/100) dØ/dt + (10/√3)(9) = 0
solve for dØ/dt
Now it's just Algebra I ...
(10/√3)(3/100) dØ/dt + (10/√3)(9) = 0
solve for dØ/dt
Now it's just Algebra I ...
Just noticed my "late-night" calculations have an errors and typos, sorry about that.
corrected version:
when 200 ft are let out,
x^2 + 100^2 = 200^2
x^2 = 30,000
x = 100√3
secØ = 200/ (100√3) = 2/√3
sec^2 Ø = 4/3
tanØ = 100/100√3 = 1/√3
then my equation should be
(100√3)(4/3) dØ/dt + (1/√3)(9) = 0
I get dØ/dt = -.0225 radians/s
check my work again carefully, still on my first coffee.
corrected version:
when 200 ft are let out,
x^2 + 100^2 = 200^2
x^2 = 30,000
x = 100√3
secØ = 200/ (100√3) = 2/√3
sec^2 Ø = 4/3
tanØ = 100/100√3 = 1/√3
then my equation should be
(100√3)(4/3) dØ/dt + (1/√3)(9) = 0
I get dØ/dt = -.0225 radians/s
check my work again carefully, still on my first coffee.