Physics solves, and the problem solving process should be detailed 30

Analysis: Because the electromotive forces of two power sources (generators, batteries) are not equal, the currents they each output are also not equal.

Let the voltage at both ends of R3 be U

It is obtained from the circuit structure in the figure.

U E1 I1 * R1 I1 is the current output by the generator in the direction of up (according to the direction shown in the figure).

U E2 I2 * R2 I2 is the current output of the battery in the direction of upwards.

U i3 * R3 i3 direction is down.

i3＝i1＋i2

Substituting the relevant data, get.

u 7 i1 * Equation 1

u * Equation 2

u i3 * Equation 3

i3 i1 i2 Equation 4

So u ]

The voltage at both ends of the load R3 is U volts.

Substituting u volts into the equation respectively.

i1 3 A, i2 1 A, i3 2 A.

Note: The values of i1 and i3 are positive values, which means that the current in the engine is actually up and the current in the load is down.

A negative value of i2 indicates that the current in the battery is actually in a downward direction (the battery is charged in the opposite direction).

The circuit is composed of e1, r1, r2, and e2, and the circuit is composed of e2, r2, and r3. The individual loops are circumnavigated in a clockwise direction.

Because the algebraic sum of the voltages in each segment of the loop is zero. The contact current is: incoming equals out.

So. For the circuit: i1r1-i2r2+e2-e1=0 for the circuit: i2r2+i3r3-e2=0 The contact current is: i1+i2=i3

Solving these 3 equations yields: i1=3a, i2=-1a, i3=2a, the negative sign indicates that the direction of the current i2 is the opposite of the assumption, and the direction of the current i2 should be downward.

The voltage at both ends of R3 is.

According to the circuit diagram, i1+i2=i3; e1-y1i1=e2-y2i2=r3*i3

Substituting the known number to solve the ternary equation.

i1 = 3, i2 = -1, i3 = 2

Voltage at both ends of load R3 = R3 * I3 = volts.

The maximum current allowed by the whole galvanometer is certain, to change to a 3 voltmeter, it is necessary to make the total resistance after modification multiplied by the maximum current (IG) equal to 3 volts, so that the total resistance is 3V divided by 3mA is equal to 1000 ohms, so that the resistance value that needs to be connected in series is 1000-RG=900 ohms.

Car S = Car V T = 12m S*2S = 24M

S sound = V sound t = 340m s*2s = 680m The driver hears the echo, and when the driver hears the echo, the car is far from the mountain S = (S sound - S car) 2 = 328m

The sound propagation distance in 2 seconds is 2s 340m s=680m, the distance of the car in 2 seconds is 2s 12m s=24m, and the distance between the car and the mountain is (680-24) 2=328m

The car whistle to hear is twice the distance, 2s (uppercase indicates the distance). If the speed of sound is 340m s, the distance is: 2s 340 = 2 s = 340 meters At this time, the car has advanced for two seconds, and the distance is 12 x 2 = 24

The distance between the mountain and the car is 328

Within 2s The distance traveled by the driver + the distance transmitted by the sound = 2 the distance from the mountain when the driver honked the horn.

The speed of the car is converted to m s, 2 12 + 2 340 = 704m = 2 The distance from the mountain when the driver honks his horn.

The distance from the mountain when the driver honked = 704 2 = 352m, and the car drove 2 * 12 = 24m after honking

So when the echo is heard, the distance from the mountain: 352-24=328m

4r 3, the velocity of the raindrop relative to the car is the sum of the two vectors, and this resultant vector is perpendicular to the windshield, just draw a picture.

Time t, the amount of rain falling on the roof is the rainwater density *r*t*s. Relative to the reference system of the car, the rainwater is perpendicular to the windshield, and the rainfall is the rainwater density * sqrt(r 2 + v 2) * t * s = rain density * 5 4 * r * t * s, and the ratio of the rainwater falling on the windshield and the roof is 5 4 under the premise that the rainwater density is isotropic

It seems that I didn't think about it comprehensively.

It's a matter of velocity synthesis versus decomposition.

Assuming that the constant right velocity of the car is v, then the raindrops have a leftward velocity component of -v with respect to the car. Make a vector triangle of velocity, which is perpendicular to the windshield of the car by the meaning of the title. So tan53°=v r v=r*tan53°

The ceiling is projected on the plane where the windshield is located, and the projection area is s*cos53°, so the ratio of the amount of water falling on the windshield and the roof is 1 cos53°

As you can see from the figure, there are 3 ropes that bear the gravitational force of an object. i.e. n=3;The total gravity of the soil plus the movable pulley = 900n + the gravity of the movable pulley = 3x tensile force; 900N + movable pulley gravity = 3x400;

Movable pulley gravity = 3x400-900 = 300n;

The mass of a man is 70 kilograms, and his gravity g=mg=70x10=700n; In order to make a person stand still on the ground, his pulling force on the equipment can only be 700N at most, according to the above calculation, it can be obtained: the maximum gravity of the soil that a person can lift is: 3x700-300=1800N; The mass is m=g=1800 10=180kg;

If the rope can withstand a maximum force of 650N; According to the above calculation, it can be obtained: the gravity of the soil that can be lifted by a person is = 3x650-300 = 1650n; Its mass is 1650 10 = 165kg

1. This is a pulley system with a labor-saving 1 3, and a pulling force of 400N can pull up the gravity of a total weight of 400Nx3=1200N. So, if the weight is 900N, then the gravitational force of the moving pulley is 1200N-900N = 300N. That is, the gravity of the movable pulley is 300 N;

2. The worker's weight is 70kg, which is the same as gravity, that is, p = mg = 75x10 = 750n. In the case of this pulley system, the maximum amount of earth gravity he can lift is p1 = 750nx3-300n = 1950n or m=p1 g = 195kg. That is, workers can lift up to 195 kilograms of soil;

3. If the rope can withstand a maximum tensile force of 650N, then the total gravity that it will be able to lift is P2 = 650Nx3 = 1950N, and the corresponding gravity of the soil is P3 = P2-300N = 1650N, which is converted into M2 = P3 G = 1650 10 = 165kg. That is, at this time, the worker is able to lift dirt weighing 165 kg.