Sophomore physics questions, ask the master to answer 10

1. When the electric key is broken, only R2 is connected in series with R1, at this time the power of R2 is 4W, R1 = 3 ohms (given the topic), we can equate R1 to resistance, that is, the current internal resistance R'= 4 ohms, according to Ohm's law for closed circuits, e=u+ir'p=ui again

That is, e=p i+ir, substituting the data 10=4 i+i*4 to solve i=2a or i=, both solutions are valid, because according to the p-r image, a power has two corresponding external resistances (when this power is the maximum power, it only corresponds to one resistance), and one resistor corresponds to one current. When the parallel resistance of R2 and R3 after the bond is closed, the current becomes larger, so the current of these two solutions corresponds to the current through R1 when the switch is disconnected, and the current through R1 is 2A when closed

2. In order to maximize the electrical power consumed by the circuit between AB in the power building S, according to the formula P=I R, because the circuit between AB is a parallel circuit and a fixed value resistance, so to maximize the power, the current of the total circuit must be the largest, and the external resistance of the power supply must be the smallest, so only when R1=0, the electric power consumed by the circuit between AB is the maximum when the power is turned on in the power building S, and the total current after closure is 2A by the first sub-question, according to E=I(R+R') is 10 = 2 (r and + 4) and r is calculated as = 1 euro. When R1=0, the total current of the circuit is 5A, so the electric power between ABs is P=25W

The difficulty of this problem lies in understanding the graph of the external resistor, the power and the resistance.

My answer] BC (double choice questions).

My analysis] This question, we will take the test (i.e., the academic level test).

Acceleration is a physical quantity that reflects how fast an object changes.

According to Newton's second law f ma, a f m, therefore, the acceleration of an object is directly proportional to the resultant external force to which it is subjected, and inversely proportional to the mass of the object, and the direction of acceleration is the same as that of the resultant external force.

Explanation of option A] Option A is wrong, the direction of velocity and the direction of acceleration have no relationship between collapse.

The direction of the Gaschanwood velocity is only the same as the direction of the combined external force.

I'll give you a counter-example: the flat toss movement.

The acceleration of the flat throwing motion does not change or the direction of the velocity.

The magnitude and direction of the change in velocity of an object in flat motion in equal time are constant.

Explain option B] Option B is correct.

The direction of velocity is constantly changing, indicating that the object is moving in a curvilinear way.

All curvilinear motion is variable speed motion).

The object moving in a curvilinear motion must have acceleration, that is, the resultant external force on the object moving in a curvilinear motion must not be zero.

You just need to understand 2 points ...

1. For the conversion of electrical energy into a single energy (may be an ideal state), such as only converted into light energy (ideal state electric lamp), only converted into kinetic energy (ideal state motor), and only converted into heat energy (ideal state resistance), in these ideal states, all power formulas are universal, that is, U2 r=i 2*r=ui=p. Once there is more than one form of converted energy, then these formulas will not be equal, and the only common formula is p=ui.

2. For electric heating alone, no matter where you go, there is only one general formula, that is, p=i 2r, and other "push-down" formulas are not valid. In an ideal state, it can be "equal", but in a physical sense, it cannot be recognized.

Current i=p u

Thermal power p1 = i 2 * r = p r u

Because the thermal power is c this.

Then d is the non-thermal power part.

b u r definitely not, this can only be used for purely resistive circuits and this doesn't make any sense.

Suppose it's 10 ohms, do you think the current represented by this formula is a few tens of amperes, and the thermal power is several thousand watts, an electric oven?

Solution: The main role of the motor is to provide kinetic energy, so electric heat is an inevitable loss.

For electric heating, only Joule's law can be calculated.

So the thermal power is i 2r

or PRU

Whereas option B says the total power of the motor.

d is the difference between the electric power consumed and the electric heating power consumed on the coil.

B answer, only related to the voltage, not the parameters of the motor, definitely not.

The answer is the effective power of the motor, and what is required now is the invalid power consumed by the heat generated by the motor itself. So it's not.

When the motor works, it converts electrical energy into mechanical energy and thermal energy, which is generated by the resistance flowing through the coil. The motor can be regarded as an ideal coil and resistor in series, so the current flowing through the motor is the heating current of the resistor. The operating current of the motor is i=p

b is an unfounded answer.

d is the mechanical power.

Remember, electric motors should not be treated as pure resistors. The motor has a total power p=ui, which is also called the power consumed by the motor. Thermal power p=i 2r, also called the power consumed by the motor coil. Mechanical power p = p total -p heat. Be sure to distinguish between these three powers.

Therefore, according to the problem, the current i=p u can be obtained, and then the coil power consumption p=i 2r can be obtained to obtain option c. Option b, you wrote a bit of a problem. Option d is mechanical power.

The voltage applied to the motor = coil voltage + motor movement voltage.

The u of b is not the coil voltage, and d is the mechanical voltage of the motor.

The motor is not a purely resistive circuit.

q proton: q tritium nucleus: q particle = 1:1:2

m proton: m tritium nucleus: m particle = 1:3:4

1) The Lorentz force provides centripetal acceleration:

qvb=mv^2/r

r=mv/qb

According to the above ratio, r protons:r tritium nuclei:r particles = 1:3:2(2)w = ek

uq=1 2mv2 v=root (2uq m) is substituted into r=mv qb

r = under the root number (2m qb2).

Substituting can obtain: r proton: r tritium nucleus: r particle = 1: root number 3: root number 2 roar, our yesterday's work was 100% correct

It seems that there is a formula for the deduction in the physics book! I forgot! Hehe!

Oh! That's right! Protons, tritium nuclei, particles (that is, helium nuclei) know what they are!

The ratio of q is 1:1:2

The ratio of m is 1:3:4

1) The Lorentz force provides centripetal acceleration:

qvb=mv²/r

r=mv/qb

Substitution yields: 1:3:2

2) There is an extra electric field to do work = kinetic energy at the end of the particle.

2uq=mv can be found for velocity v=(2uq m) under the root number to r=mv qb

r = under the root number (2m qb).

Substituting yields: 1: root number 3: root number 2

Oh! That's right! I'm not sure I'm calculating! I'm going to do the math myself!

According to r=mv qb, it is simple enough. In the second case, the kinetic energy theorem is listed first, qu=mv*2 2.

(1) v v0 = 2ax substitution: v = 5m s a = (10-6) m s

2） v²－v0²=2ax ①

t=√（2x/a）②

Syntagonism substitution: v=5m s x=

Thanks for adopting!

Analysis: (1) According to f=ma, if the mass of the warrior's body is m, the maximum resistance that the rope can provide is -6m, and the gravitational force of the warrior is 10m, which is obviously unbalanced.

So the maximum distance of the slide is.

2) The shortest time of decline t=s v=

Organize the circuit, first connect A and C together to form a circuit of (R1 R2+R4) R3, that is, R1R2 is connected in parallel first, and then connected in series with R4 to form an upper branch, and then this branch is connected in parallel with the lower branch R3, and the outer circuit resistance ohm (you can calculate it yourself).

Current of power supply output i = e (r+r)=6 3 = 2a voltmeter reading u = e - ir =

It is obtained according to the shunt formula of the parallel circuit.

The current of the upper branch is:

The current of the lower branch is.

Now pull the A and C points apart, and the ammeter is installed between the AC points, and analyze: all the circuits of the lower branch flow through the ammeter, and half of the circuits of the upper branch flow through the ammeter, and the reading of the ammeter is I'= =

Physical wolf pack.

After drawing the equivalent circuit, after the triangle-star transformation, the total resistance of the external circuit can be calculated as 36 15 ohms, so the total current of the circuit i=3 (36 15+, and the voltage is expressed as the circuit end voltage u=e-ir=3-1*

Current representation number i*(4 3)=(1-i)*(4+4 3)--i=(4 5)a

p in = vgh = 1000kg m 0 6 * 1m 0 6 s * p out = *p in =

Since the production characteristics of the power station are ready to be produced and used, the output current is:

i=p out u=

Since the allowable loss of the closed grandson is 5%, the current at the user end is i = if the power used by the user is the car

Then the ratio of the number of turns is: n1 n2=

Let the internal resistance of the noisy power supply and the ammeter be r, the internal resistance of the voltmeter is r, and the resistance of the parallel circuit is r after the external god resistor is connected in parallel'

i(r+r)=12

3i(r+r')=12

3ir'=1/3ir

r=3r12*3/4=9（v）