Thread: Sliding ladder problem

So this is an assigned problem, but I can assure you that I have tried this problem multiple times and still seem to get the incorrect answer.



If we suppose the unknown rate of change in the angle as z...

x/8 = tan z
x = 8 tan z
dx/dt = 8 sec(z)^2 * dz/dt
dz/dt = 1/8 cos(z)^2 * dx/dt
dz/dt = 1/8 cos(z)^2 * 1.3
dz/dt = 1.3/8 cos(z)^2
dz/dt = 1.3/8 (8/10)^2 <-- cos(z) is 8/10
dz/dt = 1.3/8 (64/100)
dz/dt = 0.104 rad/s

But it still says I'm wrong...? I've done the problem from the beginning a few times, and I still get the same answer. HELP!

Originally Posted by RaDeuX

So this is an assigned problem, but I can assure you that I have tried this problem multiple times and still seem to get the incorrect answer.



If we suppose the unknown rate of change in the angle as z...

x/8 = tan z
x = 8 tan z
dx/dt = 8 sec(z)^2 * dz/dt
dz/dt = 1/8 cos(z)^2 * dx/dt
dz/dt = 1/8 cos(z)^2 * 1.3
dz/dt = 1.3/8 cos(z)^2
dz/dt = 1.3/8 (8/10)^2 <-- cos(z) is 8/10
dz/dt = 1.3/8 (64/100)
dz/dt = 0.104 rad/s

But it still says I'm wrong...? I've done the problem from the beginning a few times, and I still get the same answer. HELP!

actually, tan z = y/x. but you wouldn't want to use that equation.

cos z = x/10 is better. try with that

(by the way, plugging in 8 right away is bad. not the right thing to do. if something is changing, you don't plug in a constant to begin with, because it will have a rate that shows up upon implicit differentiation. use variables to represent things that change. only plug in values if they are constant and/or you want to solve for something after doing all your differentiation and mumbo jumbo. also, per the question, it would be x = 8 as opposed to y = 8 for the instant in question).

I re-did everything. Apparently I mixed up x with an unknown number for y (not sure why I did that).

I entered -0.216, and it still said it was wrong. I get up to five guesses on the problem, so I'm not sure if I was supposed to round up to -0.217.