✔ 最佳答案
(a) Increase in kinetic energy = (1/2).(1000).(112^2 - 100^2) J = 1 272 000 J
(b) Let p be the angle at which the final velocity of 112 m/s makes with the x-axis
hence, sin(p) = 100/112
p = 63.23 degrees
The final velocity in the x-direction, Vx = 112.cos(63.23) m/s = 50.44 m/s
Using equation of motion: v = u + at
50.44 = 0 + a.(10)
a = 5.044 m/s2
Force F = 10^3 x 5.044 N = 5044 N
(c) Displacement in y-direction = 100 x 10 m = 1000 m
Displacement in x-direction = (1/2).(5.044.)(10^2) m = 2522 m
The path is a parabola starting at coordinates (0,0) and ends at (2522, 1000)
and afterwards, the path then becomes a straight line making an angle of 63.23 degrees wth the x-axis.
At 11s, the velocity remains at 112 m/s making an angle of 63.23 degrees with the x-axis.
(d) Centripetal force requred = 10^3 x v^2/[(250+6400) x 10^3]
where v is the speed at 250 km above earth surface
Hence, 10^3 x v^2/(6.65x10^6) = 10^3 x 9.1
solve for v gives v = 7779 m/s
2012-01-03 23:36:24 補充：
sorry....Displacement in x-direction = (1/2).(5.044.)(10^2) m = 252.2 m (not 2522 m)
The case is just similar to throwing a stone with an initial horizontal speed. The stone is acted under gravity, i.e. its own weight (a constant). The path is thus a parabola.
