When $A$ falls into the atmosphere at an angle $\alpha$, does the terminal velocity of $A$ return to constant? When a small meteor $A$ falls vertically into the atmosphere, the terminal velocity is constant; when $A$ falls into the atmosphere at an angle $\alpha$, does the terminal velocity of $A$ return to constant?  why?  How to force analysis?
 A: When the meteor reaches terminal velocity the forces on it are balanced. Otherwise there will be acceleration in the direction of the resultant force.
There are only 2 forces on the meteor : the atmospheric drag and its weight. When terminal velocity is reached these must be equal and opposite. The weight is always vertically downwards therefore the drag force is vertically upwards.
So regardless of the angle at which the meteor enters the atmosphere, if it reaches terminal velocity then it will always be falling vertically downwards and its terminal velocity will be the same. It is the same because there is only one speed at which the drag force equals the weight of the meteor.
Conversely if the meteor is not falling vertically downwards then you can be sure that it has not yet reached terminal velocity. 
A: 
$V$ is the direction of the meteor and $W$ is the weight of the meteor.  $W$ has two components: $W_t$ is parallel to $V$ and $W_n$ is perpendicular to $V$.  The meteor is acted on by the air, producing two components: $L$ is perpendicular to $V$ and $D$ is parallel to $V$.
 When $W_t = D$ and $L = W_n$, the meteor moves in the direction of $V$ until it burns down or falls to the ground.  This is consistent with Newton's law.
Meteors are not a standard sphere, so in some cases they will have what I said.  Even bounced back from the atmosphere to cosmic space.
