Physics knowledge contest questions for junior high school 5, physics knowledge contest questions fo

How can you just say thank you and not say the question, how can you help you?

To AThis tire can withstand a pressure of 2 atm, as the graph shows that it has reached this number, but it does not burst.

To bAt the time of t1+δt, it is exactly aligned with the "1" of the positive ordinate, indicating that the pressure of the gas inside the tire is equal to the atmospheric pressure at that time.

To CThe tires are inherently flat, and the process of inflating (in T1 time) is of course also leaking.

False DAfter the T1+ T time, the pressure inside and outside the tire is the same, so it will not continue to leak.

In this problem, B and D are opposites, and since B states that the pressure of the gas inside the tire is equal to the atmospheric pressure at that time, then D is wrong.

The teacher said that D was the right choice. a, the pressure of this tire to 2 atm is not broken, indicating that it can indeed withstand the pressure of 2 atm. c.It doesn't start to pump until T1, how do you know if the tire is flat?

The guy above has a title and no picture, which is sad.

I've already sent it to you.

My mailbox. Don't forget to pick mine.

The first big brother's topic is so simple....

Let me give you the answer, the answer is cd, as a multiple-choice question the easiest way is to find the special value, this method is simple, the detailed answer is:

First of all, this question is very important to understand that the length of the spring and the elastic coefficient are inversely proportional to the same principle, that is, the longer the elastic coefficient is, the smaller the elastic coefficient, and then explain a few problems, the first so-called length comparison between L2 and L1 is actually only a comparison of elongation, and the following is just a comparison of elongation;

First of all, l2=m1g k1+m2g k2, l1=(m1+m2)g k0, and the above two subtractions have l2-l1=(m1gk0-m1gk1) (k1*k0)+(m2gk0-m2gk2) (k2*k0).

This equation must be less than 0, because k0 is less than k1 and less than k2, k0, k1, k2, which is the corresponding elastic coefficient. Then there is how to L2 shorter, in fact, the very simple way is to think like this, put the heavier piece into the elastic coefficient, the larger the value of the division, the smaller the value, so that the larger M1, the larger K1, the shorter L2, and then change the thinking to get the answer. If you don't understand, you can ask.

Option c can be done using the special value method.

A Since it is lightweight, it does not count the mass of the spring itself, which has been done before, and it is a topic that interferes with you.

The answer is c can be analyzed using the limit method.

1) If you cut it into two along the AA line and take the upper part, the density of the object will not change, the pressure on the desktop will be reduced, and the pressure will be reduced. This conclusion is correct!

2) If you cut along the BB line and take the right part, then it will reduce the pressure on the table, and the pressure will be (unchanged).

Some car hulls are made of styrofoam as the shell, because the density of styrofoam is small, and the weight of the vehicle and ship is lighter.

1 AA pressure decreases, because the weight is less, the pressure is also reduced, the weight is small, the area does not change, and the pressure is small.

2 bb pressure decreases because the weight is smaller, the pressure does not change, the texture is uniform, and the weight subtracted changes equally with the contact area.

1 The conclusion is correct, 2 The pressure decreases, the pressure does not change, I agree with the method of the third floor, everything must be calculated by theoretical expressions, and cannot be guessed out of thin air.

1) The pressure becomes smaller, and the pressure does not change.

2) The pressure becomes smaller, and the pressure does not change.

1 The conclusion is correct, because f s = p, because f decreases, so p increases.

2 The pressure decreases, the pressure does not change, suppose 1 4 is cut off, it was originally mg s, and now it is 3 4mg 3 4s = mg s

The density does not change, the pressure decreases, and the pressure does not change 2Smaller, unchanged Foam can float on water.

1.Ultrasonic.

2.Sound travels through the air at a faster speed.

Sound travels in the form of waves and transmits energy.

Sure enough, it's a master.,I remember that it seems that the two carbon rods are connected on the line.,Accept a few more apples with Shanghai low-power bulbs that can be lit.。

Will. Ammeter.

The power supply is connected in series with R2 to get the current indicator I1, and then replace R2 with R1 to get the indicator.

i2 calculations.

Question 1: The concave surface of the spoon is a reduced inverted image, and the convex surface is a reduced upright virtual image.

Question 2: Thin strips repel each other and spread out, like a trumpet-like shape.

It is the sound made by the vibration of the column of air in the bottle, and the bottle of C has the highest pitch and the lowest of A.

Because different bottles are filled with water, his air columns are of different lengths.

The shorter the air column, the higher the pitch, and the longer the air column, the lower the pitch. The more water, the higher the pitch, and the less water, the lower the pitch.

If there is anything you don't understand, ask again. ）

1) The reason is: the friction between the trolley and the table is small, which can be ignored 2) The characteristics of the fixed pulley can be used (to change the direction of the force).

and change the magnitude of f1 and f2 by adjusting (weight mass) 3) Condition is satisfied: two forces must act on the same straight line.

1. The certainty of friction in the selection of car B is very high.

1) Replacing rolling friction with sliding friction can reduce friction.

2) Change the direction of the force of the number of weights.

3) The balance force should be along the same straight line.

Friction can be reduced by replacing rolling friction with sliding friction.

Change the direction of the force on the same straight line.

1) Rolling instead of sliding, the friction is small, which can reduce the influence of friction on the experimental results.

2) Only change the direction of the force, not the magnitude of the force.

Weight Mass 3) Two forces must act on the same straight line.