# Homework Help: Airplane landing path

1. Jun 19, 2005

### wisredz

Hi I have this question that is driving me mad any help is appreciated.

An airplane is flying at altitude H when it begins its decent to an airport runway that is at horizontal ground distance L from the airplane. Assume that the landing path of the airplane is the graph of a cubic polynomial fuction y=ax^3+bx^2+cx+dwhere y(-L)=H and y(0)=0.

(a) What is dy/dx at x=0?
(b) What is dy/dx at x= -L?
(c) Use the values for dy/dx at x=0 and x= -L together with y(0)=0 and y(-L)=H to show that

y(x)=H[2(x/L)^3+3(x/L)^2]

Anyhelp is appreciated. Thanks in advance

Last edited: Jun 19, 2005
2. Jun 19, 2005

### wisredz

Btw, that dy/dx at x=0 equals c and that dy/dx at -L equals 0 is clear to me. My problem is that I cannot use those informations...

3. Jun 19, 2005

### himanshu121

now at the top and bottom it is flat so dy/dx at x=0 and x=-L should be zero,

4. Jun 19, 2005

### himanshu121

oh u posted again,
$$y= ax^3+bx^2+cx$$
on Solving u will have c=0
Therefore
$$y= ax^3+bx^2$$
u can get values of a and b from
dy/dx at x= -L, is zero
and also y(-L) = H

5. Jun 20, 2005

### wisredz

God, it is that easy then... It was 2 in the morning here(Turkey) Thanks a lot, I was going out of my mind.