Junior 2 Physics Physics Please answer in detail, thank you 22 9 2 44

1.Milk is not pure water and contains impurities such as oil, and the specific heat capacity of these impurities is smaller than that of water, so milk with the same volume contains less water than water.

2.It is difficult to measure the amount of water contained in milk, and the specific gravity of oils and fats is smaller than that of water, so it is possible to measure the density (specific gravity) of milk to verify this from the side. For second-year junior high school students, this is the only way to go.

Because the relative density is measured, just pour milk and water of the same height into the pot and weigh them separately. That's it. The result can be seen: the same volume of water is heavier than milk.

Conjecture: The boiling point of milk is lower than that of water. Method: Put a glass of milk and a glass of water in the same environment and heat and boil at the same time, and use a thermometer to measure the maximum temperature that the two cups can rise, that is, the boiling point, for comparison.

Conjecture: The specific heat capacity of milk is smaller than that of water. Validation:

Put the same amount of milk and water of the same temperature into the sealed containers A1 and A2 respectively, and then put A1 and A2 respectively into the water containers B1 and B2 of the same shape containing the same amount of water, and measure the temperature of the water in B1 and B2 with a thermometer, and find that the temperature of B1 is lower than that of B2, indicating that the same amount of milk of the same temperature contains less calories than water. That is, the specific heat capacity of milk is smaller than that of water.

The specific heat capacity of milk is smaller than that of water.

The boiling point of milk is smaller than that of water.

The first floor should be seen clearly.

The river flows at a speed of 3 meters per second.

Solution: Let's take water as a reference first.

v*5=de:t=10 3min

1. When shared: t=5+10 3=25 3min=500s, and then take the bridge as a reference:

s=v water * t = 3 * 500 = 1500m

A: Catch up with the wooden box 1500 meters downstream of the bridge.

The car drove halfway through the journey from A to 1200 4=300s at a speed of 4m s

The car drove from halfway to B at a speed of 6m s, a total of 1200 6 = 200s, and a total of 200 + 300 = 500s

Then there are 2400 500=

Extension: This topic should be distinguished from the following types of questions:

The car drove a total of 2400m from A to B, half of which was driven at a speed of 4m s, and the other half of the time was driven at a speed of 6m s.

This kind of problem can be directly used as (4+6) 2=5m s

These two types of questions are easy to confuse, the exam should be distinguished, but also to see clearly, so much, I hope to give you some help.

As for it, the average speed is divided by the distance by the total time, and the first half takes 300 seconds, the second half takes 200 seconds, a total of 500 seconds, and the average speed is divided by 1,200 miles.

This average speed is independent of the total distance. Should be.

2/(1/3+1/5) = m/s

The first half of the journey: s1=s 2, v1=4m s =>t1=s1 v1=1200 4=300s

The second half of the journey: s2=s2,v2=6m s=>t2=s2 v2=1200 6=200s

Total distance: s=2400m t=t1+t2=500s => average speed v=s t=option c

I choose b with a diameter of 2 cm and a radius of 1 cm =

The weight is m =

50m long diameter 20cm ice weight.

Hollow part weight.

Ice actually increases:

Please give me a few points.

Power grid icing leads to breakage, inverted poles, resulting in power supply danger, last year in a snowstorm in the south of the wire ice icicles, the original diameter of 2cm of aluminum wire icing diameter reached 20cm, if the length of the wire between the adjacent two poles is 50m, answer the following questions:

Aluminium = , Ice = , = 3 )

1) The icicles formed by the wires are mainly made of c.

A is formed by water vapor liquefied b water vapor is condensed by c water is condensed by water vaporization (2) Before freezing, the mass of each wire between the two poles is.

m = aluminium v aluminium = aluminium *

3) Estimate the mass increase of each wire between the two poles after icing, m increase = ice * v ice = 900kg * [.

Sphere volume v=m p=(

In water: the ball sinks to the bottom, buoyancy f=p water * vg = (1kg dm 3) * (1dm 3) * 10n kg) = 10n

Put it in mercury:

Iron is less dense than mercury, floating, buoyant f'= gravity mg=

Equipment: iron block with mass m1 and volume v1, wool, balance, graduated cylinder.

First, measure the mass of the wooden block m2

Then tie the iron block and the wooden block together and sink it into a graduated cylinder filled with V2L water, and the reading V3 is obtained, then the volume of the wooden block v4=V3-V2-V1

Then according to the density formula =m v, we get: wood = m2 v4 = m2 (v3-v2-v1) and that's it!

Experimental equipment: balance (including weights), graduated cylinder, wooden block, water.

In the first step, the mass m of the block is measured by means of a balance.

In the second part, inject an appropriate amount of water into the graduated cylinder, and put a larger weight (greater than or equal to m) into the graduated cylinder, and the scale of the graduated cylinder is V1; Then the wooden block is lowered into the water and pressed to the bottom with a weight, at which point the graduated cylinder is graduated with V2.

The third step is calculation. The expression for the density of the block is p=m (v2-v1).

Note that my steps are concise, you can write more separately.

Just use a liquid with a density less than wood.

1 When the pressure decreases, the boiling point of water decreases.

2 solutions v = 30ml = 3 * 10 negative seventh cubic meter.

p = m v = minus seventh cubic meter = fifth power kg cubic meter.

M total = PV total = 5th power kg cubic meter * 30 cubic meters = 7th power kg

1 Decrease in air pressure The boiling point decreases.

2 I don't want to do the math 1ml of mass and multiply it by 30 if it translates to 1m3 of mass