23.(9 points) Some students used the circuit shown in Figure (a) to measure the internal resistance of a microammeter (the range is 100μ A, and the internal resistance is about 2500Ω). The equipment that can be used are: two sliding rheostats R 1, R2 (one of which has a resistance of 20 Ω, and the other has a resistance of 2000 Ω) science and technology network; Resistance box Rz (maximum resistance is 99999.9 Ω); Power supply e (electromotive force is about1.5v); Single pole double throw switches S 1 and S2. C and D are the sliders of two sliding rheostats respectively.
(1) Connect the objects in diagram (b) according to diagram (a).
(2) Complete the following blanks:
① The resistance of r1is ω (fill in "20" or "2000").
② To protect the microammeter, slide the slider c of R 1 to the position close to the sliding rheostat in Figure (a).
End (fill in "left" or "right") corresponding position; Put slide D of R2 near the middle position.
③ Set the resistance of resistance box Rz to 2500.0Ω, and turn on S 1. Put the slider of R 1 in a proper position, and then adjust the position of slider D of R2 repeatedly, so that the pointer of micro-ammeter remains unchanged before and after S2 is turned on, that is, the potential of B and D before S2 is turned on is displayed (fill in "equal or unequal").
④ Switch the position of resistance box Rz and micro ammeter, other conditions remain unchanged. It is found that when the resistance of Rz is set to 2601.0Ω, the indication of micro-ammeter remains unchanged before and after switching on S2. The internal resistance of the micro-ammeter to be used in the science network is Ω (the result is reserved to one place).
(3) Write suggestions to improve the accuracy of internal resistance measurement of microammeter.
24.( 12 points)
In order to improve the acceleration ability of ice hockey players, the distance from the coach to the starting line on the ice is s0 and S 1 (S 1 < S0), and baffles and flags are set, as shown in the figure. During training, both the athletes and the ice hockey are located at the starting line. The coach hits the ice hockey at the speed of v0, so that the ice hockey slides to the baffle in the direction perpendicular to the starting line on the ice: while the ice hockey is hit, the athletes slide from the static state to the flag perpendicular to the starting line. Training requires that when the ice hockey reaches the baffle, the players must at least reach the flag. Assuming that the athletes accelerate evenly during the skating process, the speed of ice hockey reaching the gang is v 1. The acceleration of gravity is g, and p = "">& lt/s0) is provided with baffles and flags respectively, as shown in the figure. During training, both the athletes and the ice hockey are located at the starting line. The coach hits the ice hockey at the speed of v0, so that the ice hockey slides to the baffle in the direction perpendicular to the starting line on the ice: while the ice hockey is hit, the athletes slide from the static state to the flag perpendicular to the starting line. Training requires that when the ice hockey reaches the baffle, the players must at least reach the flag. Assuming that the athletes accelerate evenly during the skating process, the speed of ice hockey reaching the gang is v 1. The acceleration of gravity is g. Seek >
(1) Dynamic friction coefficient between ice hockey and ice surface;
(2) The minimum acceleration of athletes who meet the training requirements.
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.