Urgent! Junior High School Physics Questions, Urgent !! A junior high school physics problem

341m/s。Let the speed of sound propagation in the rails be V

726 340)-(726 v)=2 is actually a solution using the equation of time difference. The speed at which sound travels in three mediums is that solids are larger than liquids and gases. Obviously, the speed in the rails is greater than the speed in the air, so there is more time in the air than in the rails.

So use 726 34o to find the time in the air, and 726 v is the time in the rails, with a time difference of 2

There is a gap between the two speeds, which is caused by the difference in the speed of the two sounds, and the time it takes for the sound to propagate in the air is obtained by s=vt

t null = s v null.

When used in iron:

t Fe = s v Fe.

The two sounds are separated by 2s, and the sound travels faster in iron than in air.

T null - t Fe = 2s = s v null - s v Fe.

Just bring in the data.

Is it detailed enough?

Known: v sound = 340m s, s = 726m, t1 = 2s solution: t2 = s v air = 726 340s

t total = t1 + t2 = 2 + 726 340s

So v rail = s t total = 726 (2 + 726 340) = 703m s Answer: The propagation speed of sound in the rail is 703m s

Then calculate the speed at which the sound travels through the rails: v=726 meters).

Option C because the bucket water is submerged in the river, so the water weight is no longer considered, which is equivalent to submerging the empty bucket in the water, and the bucket is also subject to upward buoyancy, so it is less than 38N

I hope the landlord can adopt it! Thank you!

C is less than 38n, believe in my sister, it must be right

Let the volume of A be v1 and the volume of B be v2

v1+v2=24*10^(-3)

v1*20*10 cubic kg m + 8 * 10 cubic kg m*v2 = 360 Do the rest yourself, computing ability will be a very important ability in high school in the future.

Don't do it, it's a mistake, the density of the alloy is 12 kilograms per cubic centimeter, that is, 12,000,000 kilograms per cubic meter, that is to say, the volume of this alloy is 1 cubic meter, the mass will reach 12,000 tons, such a large density is not seen on the earth so far.

20*10 cubic kg m cubic = cubic power.

8*10 cubic kg m cubic = cubic power.

A quality x B quality y

x+y=360

x However, the handicraft that Xiaohong bought turned out to be too heavy with a weight of 360kg, right?

You have a problem with the unit of this question 24 cubic centimeters 360 kilograms, the density of the alloy is greater than A and B, and the unit should be grams.

Let the mass of A be x, then B y, x+y=360

Density of x A + density of y B = 24

Note that converting the density to grams per cubic centimeter is 20 and 8 for A and B, so that A is 280 grams and B is 80 grams.

1 Start 15 minutes.

s=260m,t=15min

Speed v=s t=260m 15min=

2. 25 minutes in the middle.

s=440m,t=25min

Speed v=s t=440m 25min=

3. The whole process. Finally, the average velocity in 20 minutes is, t=20min, v=s=vt=15*20=300m

v=s/t v1=260m/900s=v2=s/t=440/1500s=

s3=v3t3= 900s=225m

v=s/t=(260m+440m+225m)/(900s+1500s+9000m)=

A: The average speed of his first 15 minutes, the average speed of the middle 25 minutes, and the average speed of the whole course is.

The pressure of the skis on the ground is equal to the total gravity of the skis and the person = 180 * 10 = 1800n

The size of the pulling force of the deer is 1800n*2%=36n