Related Rates
The sailor sails his boat at a constant speed of 12km/h staying 4km from and parallel to a straignt shoreline. How fast is the boat approaching a lighthouse on shore where boat 5km from the lighthouse?

- anonymous

- Stacey Warren - Expert brainly.com

Hey! We 've verified this expert answer for you, click below to unlock the details :)

- schrodinger

I got my questions answered at brainly.com in under 10 minutes. Go to brainly.com now for free help!

- Loser66

pic?

- anonymous

|dw:1433040585514:dw|
I'm not sure though...

- Loser66

|dw:1433040673042:dw|

Looking for something else?

Not the answer you are looking for? Search for more explanations.

## More answers

- anonymous

oh, okay

- Loser66

I think just take distance/ velocity = time

- anonymous

The 12km/h, is going negative?

- Loser66

how?

- Loser66

12km/h = 12km/ 60 minutes, that is 1minute/ 0.2 km
you have 5 km, then, it takes 25 minutes to finish the distance, right?

- anonymous

I remember something about -12km/h from my teacher, but I'm not sure though.

- Loser66

if velocity has negative sign, that shows the replacement is opposite way to what you define positive direction. In this case, they use "speed" not velocity, hence, no negative here, period.

- rational

hey still stuck on this

- anonymous

Yes @rational
I'll be right back, I have to eat dinner

- anonymous

I'm back @rational

- amistre64

so want to know the rate of change of the 'hypotenuse' of this triangle; what can we use to model the length of the hypotenuse?

- amistre64

|dw:1433045913122:dw|

- amistre64

d^2 = b^2 + 4^2
implicit derivative gives us
2d d' = 2b b'
d' = b' b/d
we know b' and b, and can determine d

- amistre64

or we know b' and d ... and can determine b either way

- anonymous

b=3?

- anonymous

|dw:1433046508888:dw|
???

- anonymous

@amistre64

- anonymous

@rational

- anonymous

Given dx/dt =12km/h, find dz/dt=? when z=5km
x^2+y^2=z^2
(2x)(dx/dt)+(2y)(dy/dt)=(2z)(dz/dt)
???

- anonymous

May the answer be 36/5=dz/dt??

- rational

36/5 looks good!

- anonymous

My teacher said something about -12km/h, but dont know why...

- anonymous

Should it be -36/5km/h?? hmmm... :/

- anonymous

@rational ??

- rational

yes, because the distance between lighthouse and boat is reducing

- anonymous

What do you mean?

- rational

in the diagram the boat is approaching near to the light house, yes ?

- anonymous

yes

- rational

since the distance is decreasing, the velocity is negative

- rational

the distance is decreasing at a rate of 36/5 km per hour
is same as saying
the distance is increasing at a rate of \(\color{red}{-}\)36/5 km per hour

- rational

i have a debt of $100
is same as saying
i have -$100

- anonymous

Oh I see! Thanks lots!

Looking for something else?

Not the answer you are looking for? Search for more explanations.