Mechanics question?

Question

I had to host the question as a image file because I couldn't fit all the info on this area, the answers are given under each question, but I don't know how to get there because I'm a new student in physics, Thanks in advance, its much appreciated!

http://img167.imageshack.us/img167/7384/mechanics2bp2.jpg

Answer 1

The glide angle can be found using energy conservation.

The energy lost in the glide over a distance d is 1340*d

This is the hypotenuse of a triangle that has a height h, which is the distance the plane must descend to maintain a constant speed.
Therefore, sin(th)=h/d
where th is the glide angle

Since the work done by friction is equal to the loss in potential energy
1340*d=m*g*h
h/d=1340/(1290*9.81)
0.105888
and the ASIN of that is
6.078 degrees

Using a bit of trig, the lift force is m*g*cos(th)
=12583.76 (rounded correctly gives 12600)

The speed of descent is
sin(th)*126/3.6 m/s
=3.71 m/s

The energy lost in that distance per second is
m*g*3.71
=1290*9.81*3.71

=46.8 kW (close enough)

b)
sin(th)=4.37/(126/3.6)
th=7.17 degrees

f*126/3.6=m*g*4.37+
1340*126/3.6

f=1290*9.81*4.37*3.6/
126+1340

f=2920 N

P=2920*126/3.6
=102 kW

I'll let you answer c

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