With the end of the 20 17 college entrance examination mathematics subject, what parents and candidates want to know most is nothing more than the answers to the college entrance examination mathematics questions. Below, I will provide you with the questions and answers of the 20 17 national college entrance examination comprehensive science paper for parents and students' reference, and wish the college entrance examination students good results this year.

25.(20 points)

There is a uniform electric field with E 1 in vacuum. In this electric field, charged oil droplets move vertically upward at a uniform speed of v0. When the oil droplet is in position A, the electric field intensity suddenly increases to a certain value, but its direction remains unchanged. T 1 After a period of time, the electric field suddenly reverses, but its magnitude remains unchanged. Branch @ Network Change; After the same period of time, the oil droplets move to point B, and the magnitude of gravity acceleration is g.

(1) the speed at which the oil drops move to point b;

(2) Find out the magnitude of the increased electric field intensity; In order to ensure that the electric field intensity in the later stage is greater than the original, the corresponding conditions that t 1 and v0 should meet are given as far as possible. As we all know, when there is no electric field, the maximum height of oil droplets thrown vertically at the initial velocity v0 is exactly equal to twice the distance between two points B and A.

The above are some questions and answers of a comprehensive science examination paper in the national college entrance examination for reference only.