There are two physics questions in junior high school. Everyone s help! Kneel and beg for urgency

To solve this problem, there are two things to know:

1) The density of water is 1kg l, which is common sense, so you have to remember it later, because you can't calculate it later if you don't know this.

2) To know the relationship between mass, volume, and density: density = mass volume, mass = density * volume, volume = mass density.

With the above knowledge, question 1 is simple. The analysis is as follows:

1）.Because the mass of the empty bottle is, and the mass after being filled with water is, then how much water is filled, obviously the mass of water is, the volume of these waters is equal to the mass of water The density of water = , this is the volume of the filled water, because it is filled with water, so this volume is the volume of the bottle, that is, the volume of the glass bottle is obtained;

2）.The mass of the metal particles is: the sum of the mass of the bottle and the metal particles minus the mass of the bottle, i.e.;

3）.At this time, if it is filled with water, then the volume of water + the volume of metal particles = the volume of the bottle, the total mass of the bottle, the metal particles and the water, remove the mass of the metal particles, and then remove the mass of the bottle, then the rest is the mass of water, that is, the mass of water is, then the volume of water is, then the volume of metal particles is the volume of the bottle (which has been calculated in question 1, is the volume of water (, that is, with the mass of metal particles and the volume of metal particles, the density of metal particles is 07

Question 2: The mass of a normal person is 65kg, and the density of water is 1kg L, if the density of a person is equivalent to the density of water, then the density of a person is about 1kg L, then the volume of a person = the mass of a person The density of a person = 65kg (1kg L) = 65L, that is, the volume of a normal person is about 65L. Or, the number of liters of a person's volume is comparable to the number of kilograms of that person's mass.

When only water is filled, the mass of the water is, and if the density is calculated as 1, the volume is the volume of the glass bottle.

The mass of the metal particles is, and then the water is filled in the bottle filled with the metal particles, which can be filled to indicate that the volume of the water is, then the volume of the metal particles is.

Density of metal =m v=

2.More than 60 More than 60.

On the first rotation, circles A and B intersect at point C, circle B rotates 1 circle, point C takes the circumference of circle A, which is exactly 3 times the circumference of circle A.

On the second rotation, the A circle actually takes a full circle at the center of the circle, and the path of the center of the circle is (1+3)r. So a spins for 4 weeks.

After the two resistors are connected in series, in order not to burn out the electrical appliance (the resistance in the question), the maximum current allowed to flow through the circuit should be amperes. So Maximum Voltage = Current Total Resistance = Volts.

Because it is not possible to burn out any resistance, the current in the series circuit is the one with the smallest, that is, ampere, so the total resistance is multiplied by the total current (the current in the series circuit is equal) (10 5).

1. Power p=40w=

Power consumption in 5 hours = kWh.

1 degree = 1000 * 3600 = so degree =

3. The current when the energy-saving lamp is shining normally:

i=p/v=9/12=

The electrical energy required for the lamp to shine normally for 10 hours:

1) e=pt=40w*5h=degree=5th power j2)e=9*10 7 j

m=e q=( ) (3*10 7)=tons.

3) Current i=p u=9w 12v=

Electric energy e=pt=9w*10h=9w*10*3600s=324000j

Divide by 1000, degrees, to the power of 7, and divide by 3x10 to the power of 7 J kg = to the power of 7.

So i = 9 12 = amp, 9 * 10 1000 remaining to the sixth power = to the fifth power.

The first way: 1 degree = 1000w·h, so 40 * 5 = 200w·h = degree 1 degree = 1000 * 3600 joules, this is calculated by yourself the second way: 9 * 10 7 * divided by the kilogram, you can convert it to the third way:

Power p=ui,i=p u=9 12=chasing the last question is the same as above,9*10 1000*

It is known that the oxygen density in the cylinder is 6 kilograms of cubic meters, and it is used to 1 3, but the volume does not change carefully.

So =m v, now v does not change the height and width, m is the original 2 3, so the remainder = 2 3 * m v = 6kg m3 * 2 3 = 4kg m3

Bernoulli's principle: The pressure of air is low where the flow velocity is high, and the pressure is strong where the flow velocity is small.

a。If you blow air horizontally under the card, of course, the air velocity under the card will be greater than the air velocity above the card, and the air pressure under the card will be smaller, and the pressure above the card will be stronger. The air pressure on it causes the card to stick to the table.

According to the relationship between fluid pressure and flow velocity, the higher the flow velocity, the smaller the pressure. Therefore, blow in the direction in the figure, the air pressure under the card decreases, and the atmospheric pressure outside will tightly press the card, and the card will stick to the desktop and not move, so choose A.

A: The card will stay flat against the table.

Choose A, you will know if you blow it.