Related rates problem help

  • #1
52
0

Homework Statement


laddercopy.png


A 1.9 metre ladder is leaning against a vertical wall. If the bottom of the ladder is 30 cm from the wall and is being pull away from the wall with a horizontal speed of 25 cm per second, how fast is the top of the ladder sliding down the vertical wall?

We define the the direction up the wall to be positive, so that your answer must be negative.

Homework Equations


[/B]
does this mean when x=30 cm dx/dt = 25


The Attempt at a Solution


[/B]
this means that the wall height is 187.6 cm using pythagoras theorem

Any help will be much appreciated
 

Answers and Replies

  • #2
cnh1995
Homework Helper
Gold Member
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does this mean when x=30 cm dx/dt = 25
Yes. Start with writing height of the ladder as a function of x.
 
  • #3
52
0
Yes. Start with writing height of the ladder as a function of x.
does this mean

h=x^2+y^2

dx/dt=2x+2y

25=2x30+2y
-35=2y
y=-17.5
 
  • #4
52
0
Yes. Start with writing height of the ladder as a function of x.
I got the answer thanks :)
 
  • #5
cnh1995
Homework Helper
Gold Member
3,442
1,147
Height of the ladder is h=√(L2-x2), where L=length of the ladder i.e. 1.9m.
You can proceed by taking derivative on both sides w.r.t. time.
 
  • #6
34,688
6,394
this means that the wall height is 187.6 cm using pythagoras theorem
The height of the wall is irrelevant to this problem.
 

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