As shown in the figure, if the power supply voltage does not change, in order to maximize the indication of the ammeter, the correct one in the following practice is () A. S1 and S2 are open B. S1 is open S2 is closed C. S1 is closed S2 is open D. S1 and S2 are closed

As shown in the figure, if the power supply voltage does not change, in order to maximize the indication of the ammeter, the correct one in the following practice is () A. S1 and S2 are open B. S1 is open S2 is closed C. S1 is closed S2 is open D. S1 and S2 are closed

It can be seen from the figure that when S1 and S2 are closed, the current path through R1, R2 and R3 is as shown in the figure below, so it can be judged that R1, R2 and R3 are in parallel, and the ammeter measures the total current in the trunk circuit; according to the characteristics of the parallel circuit, the total resistance of the parallel circuit is less than that of any branch circuit, that is, the total resistance is the minimum at this time, and according to I = ur, the current in the circuit is the maximum, that is, the current The reading of the meter is the largest, so choose D

When a body moves in a straight line with uniform acceleration, the displacements in the first two consecutive 2S are 7m and 17m respectively, and the acceleration of its motion is,

7=v0*2+0.5a*2^2
7+17=v0*4+0.5a4^2
vo=1m/s
a=2.5m/s^2

[mechanics part]
V=S/t
2. Gravity: g = mg
3. Density: ρ = m / V
4. Pressure: P = f / S
5. Liquid pressure: P = ρ GH
6. Buoyancy:
(1) F floating = f '- f (pressure difference)
(2) F = G-F (apparent gravity)
(3) , f floating = g (floating, floating)
(4) Archimedes principle: F floating = g row = ρ liquid GV row
7. Lever balance condition: F1 L1 = F2 L2
8. Ideal slope: F / g = H / L
9. Ideal pulley: F = g / n
10. Actual pulley: F = (G + G dynamic) / N (vertical direction)
11. Work: w = FS = GH
12. Power: P = w / T = FV
13. Principle of work: W hand = w machine
14. Actual machine: wtotal = w + W extra
15. Mechanical efficiency: η = w / W
16. Pulley block efficiency:
(1) , η = g / NF (vertical direction)
(2) , η = g / (G + G) (vertical direction without friction)
(3) , η = f / NF (horizontal direction)
[thermal part]
1. Endothermic: q = cm (t-t0) = cm Δ t
2. Exothermic: q = cm (t0-t) = cm Δ t
3. Calorific value: q = q / M
4. Efficiency of furnace and heat engine: η = q efficient utilization / Q fuel
5. Heat balance equation: Q discharge = q suction
6. Thermodynamic temperature: T = t + 273k
[electrical part]
1. Current intensity: I = q electric quantity / T
2. Resistance: r = ρ L / S
3. Ohm's Law: I = u / R
4. Joule's Law:
(1) , q = i2rt universal formula)
(2) , q = uit = Pt = UQ, electric quantity = u2t / R (pure resistance formula)
5. Series circuit:
（1）、I＝I1＝I2
（2）、U＝U1＋U2
（3）、R＝R1＋R2
(4) U1 / U2 = R1 / R2 (partial pressure formula)
（5）、P1/P2＝R1/R2
6. Parallel circuit:
（1）、I＝I1＋I2
（2）、U＝U1＝U2
（3）、1/R＝1/R1＋1/R2 [ R＝R1R2/(R1＋R2)]
(4) I1 / I2 = R2 / R1 (shunt formula)
（5）、P1/P2＝R2/R1
7 constant resistance:
（1）、I1/I2＝U1/U2
（2）、P1/P2＝I12/I22
（3）、P1/P2＝U12/U22
8 electric power:
(1) , w = uit = Pt = UQ (universal formula)
(2) W = i2rt = u2t / R (pure resistance formula)
9 electric power:
(1) , P = w / T = UI (universal formula)
(2) , P = I2R = U2 / R (pure resistance formula)
Common physical quantities
1. Speed of light: C = 3 × 108m / S (in vacuum)
2. Sound speed: v = 340m / S (15 ℃)
3. Echo discrimination of human ear: ≥ 0.1s
4. Acceleration of gravity: g = 9.8n/kg ≈ 10N / kg
5. Standard atmospheric pressure value:
760 mm mercury column height = 1.01 × 105 pa
6. Water density: ρ = 1.0 × 103kg / m3
7. Freezing point of water: 0 ℃
8. Boiling point of water: 100 ℃
9. Specific heat capacity of water:
C＝4．2×103J/(kg•℃)
10. Elementary charge: e = 1.6 × 10-19c
11. Voltage of one dry cell: 1.5V
12. Voltage of one lead-acid battery: 2V
13. Safety voltage for human body: ≤ 36V (not higher than 36V)
14. Power circuit voltage: 380V
15. Home circuit voltage: 220 V
16. Unit conversion:
（1）、1m/s＝3．6km/h
（2）、1g/cm3 ＝103kg/m3
（3）、1kw•h＝3．6×106J
Please list all the symbols in the above formula. Thank you
For example: volume = vm3 (M3)
Area = s square meter (M2)
Height = h m
Then just list the mechanical part and the thermal part.

1. Speed: v m / S
2. Gravity: g n
3. Density: ρ kg / m ^ 3
4. Pressure: P Pascal
5. Liquid pressure: P Pascal
6. Buoyancy:
(1) , f floating = f '- f n
(2) F = G-F n
(3) F = g n
(4) Archimedes principle: F floating = g row n
7. Leverage balance condition: F1 * L1 = F2 * L2 equation has no unit
8. Ideal slope: F / g = H / L, no unit
9. Ideal pulley: F = g / n
10. Actual pulley: F = (G + G) / n
11. Work: w = FS = GH J
12. Power: P = w / T = FV w
13. Principle of work: W hand = w machine J
14. Actual machine: wtotal = w + W extra J
15. Mechanical efficiency: η = w yes / W total no unit
16. Pulley block efficiency:
(1) , η = g / NF (vertical direction) without unit
(2) η = g / (G + G) (vertical direction without friction) without unit
(3) , η = f / NF (horizontal direction) without unit
[thermal part]
1. Endothermic: q = cm (t-t0) = cm Δ T J
2. Exothermic: q = cm (t0-t) = cm Δ T J
3. Calorific value: q = q / MJ / kg
4. Efficiency of furnace and heat engine: η = q efficient utilization / Q fuel without unit
5. Heat balance equation: Q discharge = q suction J
6. Thermodynamic temperature: T = t + 273k (Kelvin)
[electrical part]
1. Current intensity: I = q charge / Ta (ampere)
2. Resistance: r = ρ L / s ohm
3. Ohm's Law: I = u / R A
4. Joule's Law:
(1) , q = i2rt universal formula) J
(2) , q = uit = Pt = UQ, electric quantity = u2t / R (pure resistance formula) J
5. Series circuit:
（1）、I＝I1＝I2 A
（2）、U＝U1＋U2 V
(3) , r = R1 + R2 ohm
(4) U1 / U2 = R1 / R2 (partial pressure formula) has no unit
(5) P1 / P2 = R1 / R2, no unit
6. Parallel circuit:
（1）、I＝I1＋I2 A
（2）、U＝U1＝U2 V
(3) 1 / r = 1 / R1 + 1 / r2 [R = r1r2 / (R1 + R2)] ohm
(4) I1 / I2 = R2 / R1 (split flow formula) has no unit
(5) P1 / P2 = R2 / R1 without unit
7 constant resistance:
(1) I1 / I2 = U1 / U2 without unit
(2) P1 / P2 = i12 / I22 without unit
(3) P1 / P2 = U12 / u22, no unit
8 electric power:
(1) W = uit = Pt = UQ (universal formula) J
(2) W = i2rt = u2t / R (pure resistance formula) J
9 electric power:
(1) , P = w / T = UI (universal formula) w
(2) , P = I2R = U2 / R (pure resistance formula) w
Common physical quantities
1. Speed of light: C = 3 × 108m / S (in vacuum) m / S
2. Sound speed: v = 340m / S (15 ℃) m / S
3. Echo differentiation of human ear: ≥ 0.1s
4. Acceleration of gravity: g = 9.8n/kg ≈ 10N / kg N / kg m / S ^ 2
5. Standard atmospheric pressure value:
760 mm mercury column height = 1.01 × 105 pa
6. Water density: ρ = 1.0 × 103kg / m3 kg / m3
7. Freezing point of water: 0 ℃
8. Boiling point of water: 100 ℃
9. Specific heat capacity of water:
C＝4．2×103J/(kg•℃) J/(kg•℃)
10. Elementary charge: e = 1.6 × 10-19c
11. Voltage of one dry cell: 1.5V
12. Voltage of one lead-acid battery: 2V
13. Safety voltage for human body: ≤ 36V (not higher than 36V) V
14. Power circuit voltage: 380V
15. Family circuit voltage: 220 V
16. Unit conversion:
（1）、1m/s＝3．6km/h
（2）、1g/cm3 ＝103kg/m3
（3）、1kw•h＝3．6×106J

A slender spring is attached to a small ball, which is placed on a smooth table. Holding the ball, the spring is elongated, and the ball is released
B is the farthest position that the ball reaches to the right. When the ball passes through the middle position o to the right, the timing starts. If OA = OC = 7cm and ab = 3cm are measured, the timing starts from 0
In 0.2 seconds, the displacement of the ball is -----, the direction is -----, and the distance is-------
In 0.6 seconds, the displacement of the ball is -----, the direction is -----, and the distance is-------
In 0.8 seconds, the displacement of the ball is --- and the distance is-------
In 1.0 seconds, the displacement of the ball is -----, the direction is -----, and the distance is-------

7 cm, right, 7 cm;
7 cm, right, 13 cm;
0,20cm；
7cm, left, 27cm

If the current passing through the conductor is 2 A, the amount of electricity passing through the cross section of the conductor in 1 minute is 2 A_____ Cullen?

120 Coulomb

The purpose of Newton's second law experiment
Purpose of the experiment
Experimental equipment
Experimental principle (diagram)
Experimental steps
experimental data
empirical conclusion
Thank you, prawns

The purpose of the experiment is to test the relationship between the acceleration and the mass of the system when the external force is constant and the relationship between the external force and the acceleration when the mass of the system is constant

The radius of the bottom surface of a cylinder is 11cm, the height is 2.5cm, the perimeter of its side expanded view is () cm, and the side area is () cm square
Completion

The radius of the bottom surface of a cylinder is 11cm, the height is 2.5cm, the perimeter of its side expanded view is (143.16) cm, and the side area is (172.7) cm square
Bottom perimeter = 2x3.14x11 = 69.08
Expanded perimeter = 69.08x2 + 2.5x2 = 143.16
Side area = 69.08x2.5 = 172.7

As shown in the figure, one end of a spring with a length of 20cm and a stiffness coefficient of 360n / M is fixed as the center of the circle, and the other end of the spring is connected with a small ball with a mass of 0.50kg. When the ball moves in a uniform circular motion on a smooth horizontal plane at 360 π R / min, what is the angular velocity of the ball? What is the elongation of the spring in cm?

According to the meaning of the question: ω = 2 π n = 12rad / s, let the length of the spring be l, then the shape variable of the spring is: x = l-0.2, according to Hooke's Law: F = KX. ① the centripetal force required by the ball in uniform circular motion is provided by the spring's elastic force, f = ml ω 2. ② by substituting ① and ② into the data: 360 (l-0.2) = 0.5 × L × (12) 2, the solution is: l = 0.25m, so the elongation stress of the spring is 25-20cm = 5cm The angular velocity is 12rad / s and the elongation of spring is 5cm

Four mixed operations
There must be a process, preferably an answer
It's four mixed operations in primary school

1.3/7 × 49/9 - 4/3
2.8/9 × 15/36 + 1/27
3.12× 5/6 – 2/9 ×3
4.8× 5/4 + 1/4
5.6÷ 3/8 – 3/8 ÷6
6.4/7 × 5/9 + 3/7 × 5/9
7.5/2 -（ 3/2 + 4/5 ）
8.7/8 + （ 1/8 + 1/9 ）
9.9 × 5/6 + 5/6
10.3/4 × 8/9 - 1/3
11.7 × 5/49 + 3/14
12.6 ×（ 1/2 + 2/3 ）
13.8 × 4/5 + 8 × 11/5
14.31 × 5/6 – 5/6
15.9/7 - （ 2/7 – 10/21 ）
16.5/9 × 18 – 14 × 2/7
17.4/5 × 25/16 + 2/3 × 3/4
18.14 × 8/7 – 5/6 × 12/15
19.17/32 – 3/4 × 9/24
20.3 × 2/9 + 1/3
21.5/7 × 3/25 + 3/7
22.3/14 ×× 2/3 + 1/6
23.1/5 × 2/3 + 5/6
24.9/22 + 1/11 ÷ 1/2
25.5/3 × 11/5 + 4/3
26.45 × 2/3 + 1/3 × 15
27.7/19 + 12/19 × 5/6
28.1/4 + 3/4 ÷ 2/3
29.8/7 × 21/16 + 1/2
30.101 × 1/5 – 1/5 × 21
31.50＋160÷40 （58+370）÷（64-45）
32.120-144÷18+35
33.347+45×2-4160÷52
34（58+37）÷（64-9×5）
35.95÷（64-45）
36.178-145÷5×6+42 420+580-64×21÷28
37.812-700÷（9+31×11） （136+64）×（65-345÷23）
38.85+14×（14+208÷26）
39.（284+16）×（512-8208÷18）
40.120-36×4÷18+35
41.（58+37）÷（64-9×5）
42.(6.8-6.8×0.55)÷8.5
43.0.12× 4.8÷0.12×4.8
44.（3.2×1.5+2.5）÷1.6 （2）3.2×（1.5+2.5）÷1.6
45.6-1.6÷4= 5.38+7.85-5.37=
46.7.2÷0.8-1.2×5= 6-1.19×3-0.43=
47.6.5×（4.8-1.2×4）= 0.68×1.9+0.32×1.9
48.10.15-10.75×0.4-5.7
49.5.8×（3.87-0.13）+4.2×3.74
50.32.52-（6+9.728÷3.2）×2.5
51.[（7.1-5.6）×0.9-1.1