4. Bikes A and B are traveling on perpendicular roads. At the same time, bike A is

leaving the intersection at a rate of 2 feet per second and bike B is leaving the

intersection at 3 feet per second. How fast is the distance, in feet per second between

them changing after 5 seconds?

Respuesta :

Ghenji

Answer:

[tex]\sqrt{13}[/tex]

The rate of change of distance between two cars at the given time is required.

The required rate of change is [tex]\sqrt{13}[/tex] feet/s

Rate of change

a = Distance covered in 5 s by bike A = [tex]2\times 5=10\ \text{feet}[/tex]

b = Distance covered in 5 s by bike B = [tex]3\times 5=15\ \text{feet}[/tex]

c = Distance between A and B in 5 s = [tex]\sqrt{10^2+15^2}=5\sqrt{13}\ \text{feet}[/tex]

Applying Pythagoras theorem

[tex]a^2+b^2=c^2[/tex]

Differentiating with respect to time

[tex]2a\dfrac{da}{dt}+2b\dfrac{db}{dt}=2c\dfrac{dc}{dt}\\\Rightarrow \dfrac{dc}{dt}=\dfrac{a\dfrac{da}{dt}+b\dfrac{db}{dt}}{c}\\\Rightarrow \dfrac{dc}{dt}=\dfrac{10\times 2+15\times 3}{5\sqrt{13}}\\\Rightarrow \dfrac{dc}{dt}=\sqrt{13}\ \text{feet/s}[/tex]

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