physics - projectile

圖片參考：http://i182.photobucket.com/albums/x4/A_Hepburn_1990/A_Hepburn01Jan172344.jpg?t=1232207066


If you cannot see the above picture, please go to:

http://s182.photobucket.com/albums/x4/A_Hepburn_1990/?action=view&current=A_Hepburn01Jan172344.jpg



2009-01-17 23:46:01 補充：
physics8801 (001) is wrong in Q.3. He doesn't consider the gravitational field (g).

2009-01-18 10:17:13 補充：
F已經係resultant force了。發問者所問的T，正是F = T - mg
因此physics8801計漏了mg的部分，所以求出g-force了。

1. Gravitational potential energy = -GMm/R
where G is Gravitational constant
M is the mass of the earth
m is the mass of the satellite(=1000 kg)
R is the distance from the centre of the earth
Putting R = (r+ 40000)x1000 m into the equation, where r is the radius of earth (about 6400 km), and calculate the gravitational potential energy
---------------------------------------------
2. Consider the vertical component of motion and use the equation of motion, here we have,
u = 0 m/s, a = -g(=-9.81 m/s2), s = -50 m, t = ?
applying s = ut + (1/2).a.t^2
-50 = (1/2)(-9.81)t^2
hence, t = 3.1928 s
thus, the shell takes 3.1928 s before striking the sea.
Since the horizontal velocity is 60 m/s, which is unchanged during the flight. The range is
= 60 x 3.1928 m = 192 m
------------------------------------------------------
3. The mass of rocket just before all fuel has been used up
= 32000 x (1-0.85) kg = 4800 kg
Acceleration = force/mass = 400 000/4800 m/s2 = 83 m/s2
Since 1 g-force is 9.81 m/s2
thus, the acceleration of 83 m/s2 correspons to 83/9.81 g-force
= 8.5 g-force


2009-01-18 13:41:25 補充：
Your question says that the rocket is travelling HORIZONTALLY. The weight, mg, is acting vertically, and should have no action on the rocket thrust, which is acting horizontally in the same direction of the rocket.

2009-01-18 13:41:52 補充：
Likewise, the g-force, according to the question, is the g-force of the horizontal acceleration.