Answer questions 1 2 in physics. The above question is not finished. But... It should be ok..

If there is someone in the first question, let's talk about the second question. First of all, the first question, let the tensile force on the rope be t, take the ring as the research object, orthogonal decomposition, and balance the force in the vertical direction, that is, t+t30°=mg t30°=ma The acceleration of the coupling connection A The second question, take the whole as the research object, the force is analyzed, the force is f, the angle between the horizontal direction is f, the orthogonal decomposition of fsin = m total g fcos = m total a Syntagual bring in the first question to solve a You can calculate the direction and magnitude of the force, all of them are played by themselves, I hope it can help you.

Solution: Let the masses of an iron ball and an aluminum ball be a and b. respectively

From the inscription, 3a = 6b

So m:n=2:1

According to m=pv, v

Iron. =a/p,v

Aluminium. =b p, which brings the density of iron and aluminum into this formula. V iron: V aluminum.

C, because the tone of different substances is generally different, because the tone is determined by the frequency, and the frequency of different substances is generally different, when it is abnormal, the tone will be different from the normal yes, and the loudness is related to the dynamics, and the timbre cannot be used to distinguish because it is a wheel, not to mention D, so it is C

I can only say my own opinion.

First of all, d will be excluded without explanation.

After that, it depends on the magnitude of the loudness of A, and the loudness will sound a little bit if the strength is greater, and it is very unreliable to judge by loudness, so exclude A

B timbre is the characteristic of the sound, different things have different timbre, check the parts on the train, generally are damaged, the timbre will not change much.

cBecause the damage of the train parts will cause the size and length of the parts to change, and the tone will change.

I'll do I'll pick C

c Tone.

The higher the frequency at which the object vibrates.

The higher the pitch of the voice.

So the tightness of the wheels and springs can be judged according to the tone.

c.The pitch of the voice.

Judge things by timbre, and judge good and bad according to tone.

If your Na'an doesn't mean Wei'an, you can do it yourself according to my method.

The internal resistance of the header is approximately equal to 5*4.

Assuming that the police car does not move, the convict velocity v3 = v0-v1 and the bullet velocity v2 are set to be l apart from each other at the beginning

t1=l/(v2-v0+v1)

t2=(l+(v0-v1) t) (v2-v0+v1)t=t2+ t-t1=v2 t (v2-v0+v1)The above assumptions are that v2 is relative to a pistol, i.e., a police car.

If it is relative to the ground, it is (v2-v1) t (v2-v0), and the method is the same as above.