Physics Emperor, please enter, high school physics emperor.

It's just a matter of thermalism, pt·80%=cm· t

The electrical power p=1200w,c is the specific heat capacity of water, it should be known, the mass of water m=pv=120kg, t=40°c

Just find t, I hope it helps you.

Energy issues. water) MT (the amount of change in water temperature).

m = density of water * volume.

The time t can be obtained from the two formulas on the previous one

Note: c (water) = 4200 joules per kilogram of Celsius The density of water is 1000 kilograms per cubic meter.

Let the time t, the specific heat capacity of water is c (joule kilogram Celsius), the mass is m (120 kilograms), and the temperature change is 40 degrees, then there is the formula: 1200*t*80%=c*m*40. Solution t=175s=min.

The amount of heat required to heat water q = 120 l * 1 kg l * (55-15)*

Time required q = 1200 * t * 80%.

So t=

50min .120*40=1200*?。It can be concluded that it should be a multiple of 50. Based on life experience, it should be 50min.

Start by calculating the amount of energy needed to heat the water.

q=cmδt=4200j/kg℃ ×120kg ×（55-15）℃ = 20160000j

Then calculate the electrical energy.

q = 80 W electricity.

w electricity = 25200000j

The last time is calculated.

W electricity = PTT = 21000 seconds = 350 minutes = 5 hours and 50 minutes.

C: Because A and B

It remains relatively stationary, so in the process of motion B will have static friction for A, and A will also have static friction for B.

D: The force analysis knows that A is subjected to gravity, B supports A, and B rubs A. The gravitational force cancels out the supporting force, so it is the frictional force of B against A that keeps A relatively stationary in the process of motion, so the frictional force does positive work.

B is subjected to the pressure of A against B, gravity, the support force of the ground on B, the friction force of A on B before the liquid flush, pressure + gravity = support force. And the friction force of A against B is to hinder the movement of B, so the friction of A against B is judged to be negative for Zheng Li.

v to 2v, average, time t, then x=

2V to 4V, an average of 3V, because the speed of the rubber tung Natanga is unchanged, each additional 1V takes 1T, so it takes 2T

Displacement = 3v·2t = 6vt = 4x

The force is decomposed into g1 down the inclined plane and g21 down the vertical inclined plane as shown in the figureThe impulse of gravity i1 = gt = mgt = 100ns, and the direction is 2The impulse of the support force i2 = mgcos37t = 80ns, and the direction is vertically inclined upwards by 3

The impulse of the frictional force i3 = mgcos37t = 16ns, and the direction is upward along the inclined plane.

According to Newton's second law.

g1-f=ma

a=(mgsin37-μmgcos37)/m=v=at=

p=mv=44kgm/s

ig=mgt= direction: straight down.

in=nt=mgcos37 0t= direction: vertically upwardif=nnt = direction: upwards along the inclined plane.

p-0=p= i=mgsin37 0t-nnt= direction is inclined downward.

The first force analysis shows that the supporting force of the inclined surface of the object n=g*cos37=40nThe component of the gravitational force of the object along the inclined plane is g*sin37=30n, and the frictional force of the physical inclined plane f=n*u=8n

The net force of the strands is f=30-8=22n down the bottom

Then the acceleration down the inclined plane is a=f m=4, and the velocity at the end of the two seconds is v= at 4m s2

Then the momentum is i=f*t=22*2=44(i=m*v=5*As for the impulse of each force, since we know the force and the time of action, then it is very simple, and I will not make superfluous calculations.

The gravitational force of the object is 50n (take 10m s2), the inclined plane support force is 40n, the frictional force is 8n, the impulse of gravity is, the direction is vertical downward, the impulse of the supporting force is vertically inclined upward, and the impulse of frictional force is upward along the inclined plane. The resultant impulse experienced by the object is (30-8) n*2s = the impulse is a vector quantity, and the synthesis follows the parallelogram rule), according to the momentum theorem, the momentum of the object at the end of 2s is.

The gravity is straight down, and the size is 100*m

The friction force is along the inclined plane and the magnitude is 60n*m

The support force is along the inclined plane upwards and is 80n*m

The momentum at the end of 2s is given by the formula, g1-f=ma

a=(mgsin37-μmgcos37)/m=v=at=

p=mv=44kgm/s

1. The degree of heat and cold of the object.

2. No change; Boiling point; Absorbs heat.

3. Pressurization; Cooling.

4. a single line; Double line.

5. The total power is too large; Too many appliances in parallel.

6. Low-voltage electricity; High voltage.

7. a magnetic field; Force.

8. The energized conductor rotates under force in the magnetic field; Electromagnetic induction.

9. The direction of the magnetic inductance line; The direction of motion in which the conductor cuts the magnetic inductance line.

10. an electronic scale; rod scale; pound scales; bench scales; The scales ......

11. Joules.

1.How hot or cold an object is.

2.The boiling point does not change when heated (endothermic).

3.Pressurize to cool down.

4.Single-line Double-wire.

5.Short circuit Excessive electrical appliances are used, exceeding the rated electrical power.

6.Low-voltage charged high-voltage charged body.

7 .Repulsion and attraction magnetization.

8.Electrogenesis Magnetism generates electricity.

9.Electromagnetic pole direction The direction of the conductor movement.

10.Pallet balances, rod scales, bench scales.

11.Joule (j).

Reaching maximum velocity -> means positively charged -> acceleration when stopping at maximum velocity is zero - > gravity = electric field force.

The band point is uniform, and in the process of descending, more and more charges are charged on the rod entering the electric field, and the electric field force is becoming larger and larger, until it is equal to the electric field force, and then the deceleration motion is done.

If the total charge is q, then the charge per unit length is q l, and the charge entering the electric field at the maximum velocity is 1 3*q l, then there is a plex balance roll

mg=1 3*q l*e, q.

According to the volt-ampere characteristic curve, you are proportional to i because k and n are constants.

When the light is turned on, there will be a strong impulse voltage, and at this moment, it can be seen from the above equation that i will be very large.

Then from p=ui, we know that p will be very large, and the heat generated will also be very large. This can also melt the filament and cause the bulb to break.

The higher the current, the greater the voltage required.

After the first ball falls freely for 2s: x=1 2 gt1 2=1 2*10*2 2=20m

v=gt1=10*2=20m/s

Then release the second ball: the distance between the two balls is already 20m, and the speed of the first ball is already 20ms

The first ball only needs to go more than the second ball x=60m string tension The first ball displacement: x1=vt2+1 2 gt2 2 The second ball displacement: x2=1 2 gt2 2

The first ball has more displacement than the second ball: x=x1-x2=vt2t2= x v=60 20=3s

t=t1+t2=5s

It's just a matter of pursuit, it's very simple! Set the time to t

At the distance of 2 s, the velocity of the first ball is 20 m s, followed by (1) 20 t + 1 2at 2 = x1

2)10t=x2

3)x1-x2=80

Finally, find the time t.

This question is actually quite simple.

0V Obviously, the resistor is not connected to the circuit at this time.

So it's 0, and if you simplify the circuit diagram, it's easy to see.

You omitted. ==,Can you take a look at the first two questions?,I'm out of ideas.,I can help you.,Don't lie to you.,You hit the first two questions!

When S3 is closed and S1 and S2 are disconnected, the equivalent circuit diagram is shown in the following figure

Total resistance of the circuit:

r total = ui = 3v

15, r=r total-rl=15-6=9, voltage at both ends of the bulb:

ul=irl=

So the answer is: 9;

Cell phone!!! Your picture is too small to see clearly!!