Answers to Physics Questions in the Fourth Year of Junior High School!!! Hurry, hurry

1. There is no formula for this.

1200r kW·h——— that is, 1200 rpm means 1kWh of power. Power consumption per revolution is: 1 1200 kWh

Now after 55 revolutions, the power consumption is: 1 1200 kWh 55 = 11 240 kWh

2. W=pt=U 2 rt=(220V) 2 Euro 300S=30000J

3. The title should be parallel.

1 The current through R1 is: i1 = U R1 = 12V 6 ohms = 2A

The electrical power of R1 is: W=UIT=UI1T1=12V 2A 60S=1440J

2) The current through R2 is: I2=U R2=12V 12ohm = 1A

The total current in the current is: i=i1+i2=3a

According to the title: w=uit=12v 3a t2 =10800j

The solution yields t2=300s

4. According to the title.

w= uit=6v × i ×60s=180j

Solution i=

Based on the information given in the question, we can get the following calculations:

The power of the electrical appliances is 480 10 = 48 kW.

The resistance of the appliance is 2400 48 = 50 ohms.

To sum up, the power of this appliance is 48 kilowatts and the resistance is 50 ohms.

Based on the information given in the question, it can be concluded that the electricity consumed by running the appliance for 10 minutes is 480r 2400r kWh = .

The p (power) of an appliance can be calculated by p = e t, where p is power, e is energy, and t is time. Therefore, the power of the consumer can be calculated by p = 10min = .

The r (resistance) of an appliance can be calculated by r = v i, where r is the resistance, v is the voltage, and i is the current. Because the values of voltage and current are not mentioned in the question, it is not possible to calculate the resistance of the appliance.

To sum up, the power consumed by an electrical appliance running for 10 minutes is , and the power is .

Let me give you the meaning of this question first.

Left Mountain: "=a=", people, "=b=", Right Mountain.

When a person shouts, the sound touches the left mountain, reflects it to the human ear, passes through the human ear, and reflects back from the right mountain. In essence, it is two round-trips between the two mountains. The time difference is 1 2b-a, and the distance difference is 1 2(b-a)v.

Therefore, the solution to this problem is: s=vt=1 2*

b a: The nuclear charge number of this atom is 1

c There is 1 electron outside the nucleus, and the number of electrons is equal to the number of protons.

dThe nucleus has a positive charge of 1 unit.

Keep in mind this conclusion: when sinking to the bottom (both submersion and sinking can be used) liquid density: object density = buoyancy: gravity bring it in and the result comes out.

The density of the object should be.

Find the mass of the object m=g=39 10=

Find the volume of the object v=m v=. 5 cubic meters.

The buoyancy force experienced by the object f=g-f=39-34=5n

Liquid = f float vg = 5n

Hope it helps.

1.When the tires of the truck leak, the pressure of the truck on the ground will become larger, B will become smaller, C will not change, and D cannot be judged.

Choose B, become smaller, because the area of the ground becomes larger, the pressure remains the same, the area becomes larger, the pressure becomes smaller) 2A person with a mass of 68 kilograms, whose area of each foot touches the ground is 170 square centimeters, then the pressure on the ground when walking is - Pa (g = 10 n kg).

One foot bears the gravitational force of the body. p=f/s=68x10/170=4kg/cm^2=40000pa

3.A ballet dancer performs with a negative 4th power of 8 times 10 with the contact area of her toes with the ground, and her pressure on the ground is close to.

To the fifth power of the cubic power.

Question 1: a

Analysis: The pressure is only related to the pressure and the contact area, the pressure on the ground when the truck is leaking is unchanged (the weight of the car is unchanged), and the contact area between the tire and the ground is also unchanged, so the pressure of the car on the ground is unchanged.

Question 2: p=f s (pressure equal to positive pressure divided by force area).

f=mg=68x10=680n (the amount of pressure on the ground is equal to the amount of gravity of the person).

S = people walk with only one foot in contact with the ground, so the ground force area is only 170 square centimeters, pay attention to the basic unit in the national strength unit system).

The result is more or less your own.

Answer to question 3: d

Analysis: According to common sense, the weight of a ballet dancer is about 50kg-60kg, so her pressure on the ground is about 500n-600n, and her contact area with the ground is, so according to the formula for calculating the pressure p=f s, it is easy to calculate her pressure on the ground to the fifth power of the order of magnitude of 10.

After answering, I hope it will be helpful to you.

1. The pressure P=F S, the pressure F remains unchanged, and the S becomes larger when the air leaks, so the pressure becomes smaller, choose B2, when walking, it can be regarded as landing on one foot, G=MG=68KG*10N KG=680N, S=170 square centimeters = square meters, and then calculate it with the pressure formula, and then you can calculate it, right?

3. The weight of a ballet dancer can be estimated to be about 500N, which is used as pressure, and then calculated by using the pressure formula.

1.Because the pressure in this case is equal to gravity.

2.As with the above reasoning, gravity equals pressure.

3.The same goes for ...

The contact area between the wheel and the ground becomes smaller, the same weight, the smaller the force area, the greater the pressure 170 square centimeters = square meters.

p=68 帊.

The three questions can't be done without a unit.

1. b becomes smaller because the gas runs away and the mass decreases.

10 (170 10000)=40000pa f s=p Walk with one foot on the ground.

3. According to the previous question, the area is now 8 square centimeters, and the area of the previous question is 170 square centimeters, and the area has decreased by nearly 20 times, because the pressure is inversely proportional to the area, so the pressure has increased by nearly 20 times. 40000 20 = 800000, answer D

because the stressed area increases.

Divide by 10000) = 40000pa

3.The estimated actor weight is 48kg, p = 48 * 10 8 times 10 to the negative fourth power = 6 * 10 5 times.

So for d

w=f*s=20*3=60j

0j (no vertical movement, gravity does no work).

f=20n (because of constant velocity).

1. The thermometer touched the wall of the cup, and it was not thrown below 0 degrees before use.

3. Measure the weight when wet, and re-measure it over time.

4. Hot water fast.

5. Tie a small hole in a bottle cap, and put a black piece of paper behind it, usually block the small hole, and let it go when taking pictures.

It may be more beneficial to look for books and materials on your own.

To be honest, if you add a 0 after the bounty, I will write all the questions to you accurately without saying a word.

But it's too tiring to do this for ten points, so let's skip it.

1. Exothermic when melting.

The same or similar answers can be found in the book for all other lab questions.