[Rules]
Two objects do throwing body movement , the acceleration is the same, and the two objects are relatively moving in a uniform linear speed, but attention should be paid to the constraints.
Two objects do flat throwing motion four points note:
(1) If two objects are thrown from the same height (or the same point), then the two objects are always at the same height. The spacing between the two only depends on the horizontal movement of the two objects;
(2) If two objects are thrown from different heights at the same time, the height difference between the two objects is always the same as the height difference of the throwing point. The spacing between the two objects is determined by the horizontal movement and the vertical height difference of the two objects;
(3) The two objects are thrown one after another from the same point. The vertical height difference between the two objects gradually increases with time. The spacing between the two objects depends on the horizontal movement and vertical movement of the two objects;
(4) The intersection of the two flat throwing motion trajectories is the possible encounter between the two objects. To meet here, the two objects must reach here at the same time.
Example: When in the park, we often see a game that both adults and children like to play - a "circle". As shown in the figure,
is the scene of the "circle" game. Suppose a child and an adult throw two small rings horizontally from different heights from the ground on the same vertical line. The height when an adult throws the ring is 9/4 times the height of the ring thrown by the child, and as a result, they all happen to be trapped in the same object on the ground. Excluding air resistance, the ring (C) thrown by adults and children is
A. The ratio of exercise time is 9:4
B. The ratio of speed change rate is 4:9
C. The ratio of horizontal initial velocity is 2:3
D. The ratio of speed when landing is 3:2
Example: There is an rugby aerial fencing game in CCTV variety show "Come on to the future":
Sword falls freely from point B in the air, and the rugby is thrown in the direction of AB at speed v₀, just in the air C clicks the tip of the sword, regardless of air resistance. The correct statement is ()
A. The acceleration of the rugby in the air is greater than the acceleration of the sword falling
B. If the rugby is thrown in the original direction at a speed less than v₀, it will definitely hit the sword tip below point C
C. If the rugby is thrown in the original direction at a speed greater than v₀, it will definitely hit the sword tip above point C
D . No matter how fast the rugby is thrown in the original direction, it can hit the tip of the sword
[Analysis] The two objects have the same acceleration, and they are relatively uniformly tempo linear motion , v₀ is large, the hit time is short, and it will be above point C. v₀ is too small and the hit time is long. In theory, no matter how fast the thrown in the original direction, it can hit the tip of the sword, but the encounter point will be below the ground.
Example: As shown in the figure,
has two points A and B with a distance of L on the horizontal ground. The ball A is thrown up from point A at an initial velocity of v₁=10m/s in a direction at a 30° angle to the horizontal direction, and the ball B is thrown up vertically from point B at an initial velocity of v₁=10m/s. If A meets B at the highest point and the gravity acceleration g is 10m/s², then the correct statement is (ACD)
A. The initial velocity of ball B must be 5m/s
B. The speed of ball A before encountering may be less than the speed of ball B. L is 2.5√3m
D. Ball A and ball B are always on the same level
Example: "Oriental 1 2018" is a joint military exercise between China and Russia, which started on September 11, 2018. As shown in the figure,
In the joint military exercise, aircraft above the ground H at a horizontal speed v₁ Launch a bomb to bomb the ground target P. The sensitive ground interception system simultaneously fires a shell vertically upward at the initial velocity v₂ to intercept (the shell movement process is considered to be vertically upward). At this time, the horizontal distance between the interception system and the aircraft is x. If the interception is successful, regardless of air resistance, the relationship between v₁ and v₂ should meet (C)
Example: As shown in the figure,
each blows soybeans with straws. As the soybeans A are shot horizontally from point P at the end of the straw, and soybeans B are shot up obliquely from point M at the end of the other straw. After a period of time, the two soybeans meet at point N. Curves 1 and 2 are the movement trajectories of soybeans A and B respectively.If point M is directly below point P, point M and point N are on the same horizontal line, and the PM length is equal to the length of M, regardless of the air resistance of soybeans, you can regard soybeans as particle , then (A)
A. When two soybeans meet, the tangent value of the angle between A and the horizontal direction is twice that of B
B. The velocity of soybeans at point P is not equal to that of soybeans at the highest point
C. When two soybeans meet, the velocity of A is twice that of B
D. The maximum height of B soybeans rise relative to M point is half the length of PM
[Analysis] Soybeans shot horizontally from point P are used to throw flat, and soybeans shot diagonally upward from point M are used to throw obliquely. The two meet in the air. Since they are shot at the same time, the end position N point is the same, so the two soybeans move equally, the horizontal displacement is the same, and the horizontal velocity is the same. The soybeans in B are slanted to throw, which has symmetry.
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-