Grade 8 physics questions, begging for people, urgent, really urgent, begging for people

The first is to judge from the point of view of time.

The time when the rabbit escapes into the hole t=s v=50 18=......The time when the eagle catches the hole t=s v=160 45=......If the eagle has a long time, it means that the rabbit has entered the hole, and the eagle is still flying in the sky!

The second, judging by the distance the eagle flies.

If the rabbit enters the hole, the running time can be found (see the first method), then the distance the eagle can fly during this time s=v * the time the rabbit runs into the hole = ......

Comparing this distance with 160 meters, it can also be judged. If it is more than 160 meters, it means that the rabbit has not entered the hole, and the eagle is waiting for him at the entrance of the hole.

Third, if the eagle flies to the hole, calculate the distance the rabbit runs to judge.

The flight time of the eagle t = s v = 160 45 = ......The distance that the rabbit can run at this time is s=vt=18*t=......Compare this distance with 50 meters, if it is larger, it means that the eagle has reached the entrance of the hole, and the rabbit has already entered the hole.

It is not easy to answer the question, I hope to help the landlord.

The first method: t rabbit = s rabbit v rabbit = 50m 18m s = t eagle = s eagle 1 v eagle = (110m + 50m) 45m s = the rabbit runs into the tree hole less than the eagle chases the rabbit. So the rabbit will not be caught by the eagle.

The second method: find the t rabbit first, S eagle 2 = V eagle * T rabbit = 45m s* Because S eagle 1 is greater than S eagle 2, the eagle cannot catch the rabbit.

If you have any questions or mistakes, please let me know. Thank you.

1. When S is closed, i=u1 r1 bidisson r1 r3=u1 u3=1 4

i=u3/r3 ②

When s is disconnected, i=u1'r1 Contra r1 r2=u1'∶u2'＝1∶2 ⑥

i=u2'/r2 ④

Synoid r1 r2 r3 = 1 2 4

Set the power supply voltage to U; r1=r;then r2=4rr3=4r

i=u/5r i∶i'=7∶5

i'=u/7r

u1=ir u1'= i'r u1∶u1'= i∶i'=7∶5

u3=4ri u3'=4ri' u3∶u3'＝7∶5

So option d is correct.

Second, it is known that t=60s, q=36c, w=18j

i=q/t=

w=i²rt=18 r=5ω/6

u=ir=don't know how to ask again.

Hope it solves your problem!

When boiling water is poured into the bottle, the air in the bottle will vibrate and make a sound due to the agitation of the water flow, and the air column is longer at the beginning, the vibration frequency is small, and the sound is low-pitched; The more water is filled, the shorter the column of air, the greater the vibration frequency, and the higher the pitch of the sound produced.

Example: Cold water pours on the ground with a crisp crackling sound, while boiling water pours on the ground with a low fluttering sound. This is due to the fact that there is a lot of air in cold water, and there is almost no air in boiling water.

The volume of air is reduced, and the sound of boiling water in a boiling water bottle is produced by the vibration of the gas inside the bottle.

1. The pressure of water on the bottom of the container is found by the liquid pressure formula.

Solution: The pressure of water on the bottom of the container is: p=pgh=

2. The pressure of the container on the horizontal table is calculated by p=f s.

Solution: From the meaning of the question, it can be seen that the pressure of the container on the horizontal table is .

f=20n+10n/kg*18kg=200n.

So the pressure of the container on the horizontal table is .

p=f/s=200n/2*10^-2m=10^5pa.

This is a student's book, and I'm looking for it! Just found.

Table tennis balls are used to represent the moon and soccer balls are used to represent the earth!!

A car weighing 1.2 times 10 to the fourth power of Newton travels at a constant speed on a straight road, and the car is in motion (in equilibrium), then the ground supports the car for ( ) Newton, and the pressure of the car on the ground is ( ) Newton; If the power of the car is 75 Newtons, then the frictional force experienced by the car is (75) Newtons.

（1）a.The length of the thinner straight tube is cut to 5 cm, and a convex lens B. is inserted at one endCut a thick paper tube into 5cm, and seal one end with plastic film CI was still thinking about connecting 2 paper tubes together and adjusting the length until an image (2) was displayed on the film.

3) Imaging is inverted and zoomed out.

1 Material preparation.

1 convex lens (focal length within 10 cm), 1 piece of 10 cm 8 cm of ground glass, 1 sheet of thin cardboard, 1 bottle of glue, 1 pair of scissors, and a number of horse manure paper

2 Steps.

Make the camera obscura: fold the cm jammer frame with thin cardboard, glue the seams firmly, and the four corners can be folded into triangular prisms with horse manure paper to bond and reinforce

Fixed image screen: Use thin cardboard to make a frame for ground glass (see Figure Light-13), and leave a 1 cm wide strip at the edge of the frame, so as to be folded outward and fixed in the camera obscura

Make the lens tube: use thin cardboard to make the frame of the convex lens, and then use thin cardboard to make the lens tube, the lens tube is divided into two parts: inside and outside, the outer lens tube can be moved back and forth in the inner tube can be moved back and forth The front end of the inner lens barrel is fixed with a convex lens, and the method of fixing the lens refers to the method of fixing the image screen The length of each lens barrel is 3 4 cm

To make the panel: cut out 1 piece of horse manure paper of 11 cm and 9 cm, dig out a round hole with the same diameter as the outer lens at the intersection of its diagonals, and fix the outer lens barrel on the round hole, and then fix the panel on the camera obscura

Seal the light leakage of the camera obscura and panel

Insert the inner cylinder of the lens into the outer cylinder and adjust the position of the lens back and forth, while observing the image on the frosted glass until the image of an object in the field of view is clear

The result is like an upside-down, shrunken reality.