It s so hard!! Logical physics masters!!!!

C, the reading is inaccurate because alcohol is volatile, and when it volatilizes, it will take away the heat in the surrounding environment, resulting in a decrease in temperature (don't believe yourself if you apply some alcohol on the back of your hand, you will also feel cold) and the reading should theoretically be lower than A and B, so C is not accurate.

Design experiment: The same three thermometers, still the same number

Put it in the refrigerator, set the temperature of the refrigerator to a value (not exceeding, the temperature measurement range) put A, B C together, and observe the reading after a period of time, and the results are clear at a glance

Third. Reason: The alcohol in the beaker is evaporating and absorbing heat.

The temperature is lower than room temperature.

B in a closed alcohol bottle and does not evaporate. No heat dissipation.

Put C only in the air.

A thermometer with inaccurate readings is C.

Because alcohol volatilizes, it lowers the surface temperature of the object.

B is placed in an airtight alcohol bottle, and the alcohol does not volatilize.

A thermometer with inaccurate readings is C.

Rationale (the alcohol in the beaker of alcohol volatilizes and takes away heat) Design an experiment to prove your conclusions:

1.Read the thermometer at room temperature, 2Placing a thermometer in the water (completely submerging the mercury ball) readings gives degrees 1 and 2 being the same, 3When you take out the thermometer that has been placed in the water, you can see that the degree of the thermometer is dropping.

The answer has been said before, but no one seems to mention verification.

I have a solution:

Place the thermometer in an ice-water mixture or in boiling water (at one standard atmosphere) to see if the temperature is 0 or 100 degrees Celsius.

Liminqiang2003 - Xiucai Level 2.

No. 3): It should also be: take out the thermometer put in the water, and you can see that the degree of the thermometer is (rising)!! However, your experiment should have been done in the winter!!

Dizzy, such a question is also super difficult ......(Comrades still need to work hard).

Minute hand solution speed: 1=(2) t1=(2) 60

Hour hand solution speed: 2=(2) t2=(2) 12*60).

The catch-up time is one turn angle divided by the relative angular velocity: dt = (2) 1- 2) = 720 11

It can be regarded as a mathematical catch-up problem, and let the two needles come together as 1, the hour hand speed is 1 (12*60min), and the minute hand speed is 1 60min

1/（1/60-1/12*60）=a

Angular velocity of the minute hand 1 60 rad min

Hour hand angular velocity 1 720 rad min

Let the time elapsed from the coincidence of the two stitches to the second coincidence x

then 60min x 120mim

The instant needle went a little more than a circle.

1 60)*x-1=(1 720)*x, simplified to x=720 11

Maybe it's obscene, but my brother has to teach you. As we can imagine, the minute hand rotates for one hour and the hour hand moves one block (1/12th of a turn), so the actual overlap time must be more than 65 minutes.

Then B, C, and D are eliminated directly.

Although the previous brother's answer is very accurate, it lacks practical associations and is not suitable for the rhythm of the test.

The maximum static friction and sliding friction are both mg=

When an object moves to the left, it must be subjected to sliding friction, which is 100n in magnitude and direction to the right.

The team will answer for you.

The chest moves to the left, so it experiences a sliding friction f from the right, and f = n=.

When the speed is reduced to 0, the sliding friction disappears; Due to the 50n tension to the right, a static friction force of 50n to the left is generated!

This problem is a problem of the high school kinetic energy theorem: the work done by the combined external force is equal to the change in the kinetic energy of the car wf-wg-wf ek

fl-mgh－fl=1/2mv^2

2900*100-27500*5-f*100=1 2*2750*10 2,10m s is the converted speed, and f can be found

(1) The maximum force that the student can exert:

F large = g stone = m stone g = 30kg 10n kg = 300n;

When the student moves pebbles in the water, the maximum gravity that can lift the pebbles in the water:

g large = f float + f large, let the volume of the pebble be v, then stone vg = water vg + f large, that is, the solution: v = 2 10 2m3, the maximum mass that can be lifted in the water at most:

m= stone v=;

2) The buoyancy of the stone at this time:

F float = water v row g = water vg = 1 103kg m3 2 10 2m3 10n kg = 200n

So the answer is: 50; 200．

Hope it helps

Friends who ask questions on the mobile phone, please comment on the [satisfied] in the upper right corner of the client. Your adoption is the driving force for me to move forward

1) The pressure of alcohol on the bottom of the cup = alcohol density * liquid height * gravitational acceleration = (2) The pressure on the table = (the gravity of alcohol + the gravity of the cup) The area of the bottom of the cup = 3500pa

Hope it helps.

I forgot the formula for high school but can tell you how to do it.

The first question: If the rope is to break, the tension on the rope must reach the maximum. Since it is doing a circular motion, the tension on the rope is greatest at the very bottom position, and it is equal to the gravitational force of the Bear II plus the centripetal force of their circular motion.

In this way, we can find the velocity of the chest bear two when reaching the bottom of the point, according to the conservation of energy, regardless of friction, according to the kinetic energy of the lowest point equal to the neutral potential energy of the highest point, find the height, and then find the answer according to the knowledge of simple circles and the solution of right triangles.

Question 2: This is a problem of flat throwing motion, and its understanding is: in the horizontal direction, it can be regarded as a uniform linear motion, and in the vertical direction, it can be regarded as a free fall motion with a velocity of 0.

For this problem, you can find the time of free fall, and then according to the principle of isochronousness, you can know the time of uniform linear motion in the horizontal direction, and you can find the distance of a uniform straight line, which is the distance.

Problem 3: Hypothetical method, assuming that the speed of reaching the lowest point at this time is v, you can calculate the rope length (algebraic formula with v) and you can find the time of falling (algebraic formula with v), and the horizontal distance is equal to 5m to solve v to see if there is a solution, or see if the rope length represented by v is satisfied with the topic. (The third question may be the ideal method, because there is a cubic shape, it may not be feasible, so you have to think differently, because I have graduated from high school for many years, and I forgot the formula, so I didn't do it myself, but I hope it will help you).

1. The centripetal force is the combined external force.

2.After the break, there is a flat throwing movement.