14. As shown in the figure, a large smooth ring is fixed on the desktop, and the ring body is located on the vertical plane. A small ring is sleeved on the big ring, and the small ring starts to slide down from the highest point of the big ring. In the process of sliding down, the big ring acts on it.
A. never work
B. always do positive work
C. always point to the center of the great circle.
D. always deviate from the center of the great circle.
The answer to this question is B.
17. As shown in the figure, the semicircular smooth track is fixed on the horizontal ground, and the diameter of the semicircle is vertical to the ground. A small object slides into the orbit from the lower end of the orbit at a speed v and flies horizontally from the upper end of the orbit. The distance from the rapid landing point of small objects to the lower end of the trajectory is related to the trajectory radius. When this distance is maximum, the corresponding trajectory radius is (g).
Audio and video? / 16g B.v？ /8g C.v？ /4g D.v？ /2g
The answer to this question is B.
19. As shown in the figure, Neptune orbits the sun in an elliptical orbit, with P as perihelion, Q as apohelion, M and N as the two endpoints of the short axis of the orbit, and the running period is T0. If we only consider the interaction between Neptune and the sun, Neptune is in the process from P to M and Q to N.
The time from p to m is equal to T0/4.
B. from q to n stage, mechanical energy gradually increases.
C. from p to q, the speed gradually increases.
D from m to n, gravity does negative work on it first, and then positive work.
The answer to this question is CD.
The above are some of the questions and answers in the two-volume science comprehensive examination paper of the national college entrance examination for reference only.