Respuesta :
Answer:
[tex]\frac{dz}{dt} = 65 mi/h[/tex]
Explanation:
let distance between two cars is = z mi
we have to find =[tex]\frac{dz}{dt}[/tex]
One travels south at = 60 mi/h = [tex]\frac{dx}{dt}[/tex] (given)
the other travels west at =25 mi/h.= [tex]\frac{dy}{dt}\\[/tex] (given)
since both car have constant speed
at t = 3 hrs
x = 3× 60 = 180 mi/h
y = 3 × 25 = 75 mi/h
from the figure (i) we get
[tex]z = \sqrt{( x^2+ y^2)}[/tex] ...............(i)
put x and y values
we get
[tex]z = \sqrt{(180)^2 + 75^2}[/tex]
[tex]z = \sqrt{32400 + 5625} \\z = \sqrt{38025} \\z = 195 mi/h[/tex]
differentiate the equation (i) w r to t
[tex]z^2 = x^2 +y^2[/tex]
[tex]2z\frac{dz}{dt} = 2x\frac{dx}{dt}+ 2y\frac{dy}{dt}\\[/tex]
put each values
[tex]2 \times195\frac{dz}{dt} = 2 \times 180\frac{dx}{dt}+2 \times75\frac{dy}{dt}\\[/tex]
[tex]2 \times195\frac{dz}{dt} = 2 \times 180\times 60}+2 \times75\times25\\\frac{dz}{dt} = \frac{{2 \times 180\times 60+2 \times75\times25}}{ 2 \times195}\\\frac{dz}{dt} = 65 mi/h[/tex]
