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Dirac.

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Dirac.

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lurflurf

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let x(t), y(t) be the distance respectively from the wall and floor.Dirac said:

Dirac.

1) relate x and y

2) differentiate the relationship to relate x' and y'

3) find write y(t) in terms of t then find x(t),x'(t),y'(t)

4) use x(ti)=3 to find x'(ti)

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Could you please do a step-by-step solutionlurflurf said:let x(t), y(t) be the distance respectively from the wall and floor.

1) relate x and y

2) differentiate the relationship to relate x' and y'

3) find write y(t) in terms of t then find x(t),x'(t),y'(t)

4) use x(ti)=3 to find x'(ti)

Dirac.

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lurflurf

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No.Dirac said:Could you please do a step-by-step solution

Dirac.

so the ladder, a piece of floor and a piece of wall form a right triangle.

where the legs are x,y and the hypotenus is 5 can you write an equation relating these quantities?

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Yes, ok but what is x(t)lurflurf said:No.

so the ladder, a piece of floor and a piece of wall form a right triangle.

where the legs are x,y and the hypotenus is 5 can you write an equation relating these quantities?

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HallsofIvy

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Yes, I can do it, but I get two solutions for t fromHallsofIvy said:

(x^2)=5t-0.25(t^2)

Dirac.

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lurflurf

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x is the distance from the bottom of the ladder to the wall measured along a line along the floor that is perpendicular to the wall.Dirac said:Yes, ok but what is x(t)

y is the distance from the top of the ladder to the floor measured along a line along the wall that is perpendicular to the floor

also I am assuming the wall is perpendicular to the floor

thus we have a right triangle with legs x,y and hypotenus 5

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I get from your values that the velocity of the sliding is 0.333m/s. But dont quote me!!!

I f you show me your working perhaps i can help

hhh79bigo

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By Pythagoras'

(x^2)+(y^2)=(r^2)

y=5-0.5t

r=5

=>(x^2)=25-(25-5t+0.25(t^2))

=>(x^2)=5t-0.25(t^2)

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Oh ok, done it now.

Dirac.

Dirac.

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lurflurf

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x and y should be positiveDirac said:Yes, I can do it, but I get two solutions for t from

(x^2)=5t-0.25(t^2)

Dirac.

then there is only one solution

There is also an easier way

we know

x*x'+y*y'=0

so

x'=y*y'/x

we know y'=-.5 x=3 y=4 so x' is easy to find

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HallsofIvy

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And you STILL haven't shown us what you have done! Don't just give us your (wrong) answer. Show us how you got it.Dirac said:Yes, I can do it, but I get two solutions for t from

(x^2)=5t-0.25(t^2)

Dirac.

In fact, your answer makes no sense. The problem does not even ASK you to find t! If you let x be the distance from the wall to the foot of the ladder, the problem asks you to find dx/dt.

Now do what lurflurf suggested to begin with: Draw a picture, look at the right triangle in the picture and write an equation relating the parts of the picture. That will be a "static" equation- your picture is kind of like a snapshot of the sliding ladder. To get a "dynamic" equation (a moving picture) differentiate the entire equation with respect to t (even though there is no t in the equation!)

For the same reason, the answer to hhh79bigo's question is "No, that makes no sense at all- you were not asked to find the time the ladder takes to fall to the floor."

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Forgive me for being ignorant

I apologise I thought that the top of the ladder was 5m of the ground

hhh79bigo

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