What is the main function of periscope in military_____________________________ .

Is periscope underwater? If it is, it uses the refraction of light (in a right angle, similar to the rear lamp of a bicycle) to see the situation on the water, so as to avoid being found by the enemy. The principle and function of periscope on land are the same,

In order to remind drivers of driving safety, warning signs of "slow down and slow down" are set at the corners of expressways. Please briefly explain the physical truth contained in the warning signs
Attention! It's the corner of the freeway! Please answer carefully,

In addition to the gravity and traction force, the car at the corner will also be subject to the centrifugal force of the center of the arc pointing to the car's trajectory. The centrifugal force is f = MV (quadratic) / R. when the speed is very fast, f will be very large, which is easy to cause the car to roll over

Urgent need
A man is 1.6 meters long, and there is a mirror two meters in front of him. How big is the smallest mirror to let him see his whole body in the mirror?
Note: there is a mirror two meters in front of him,
It's urgent
PS: there should be a problem-solving process and Analysis
It might be a bit of a problem

Answer: half the height, 0.8 meters
The distance from the object to the mirror = the distance from the virtual image to the mirror = 2m
Distance from virtual image to human: distance from mirror to human = (2 + 2): 2 = 2:1
So the height of a person: the height of the mirror = 2:1
(ratio of bottom edge of similar triangle = ratio of height)
The mirror should be at least x meters long
2:1=1.6:x
X = 0.8m

A and B are two rolls of thin copper wire with different thickness. The label of a roll of copper wire indicates that the diameter is 0.8mm. The label of B roll has been blurred. Without a scale, what simple method can you use to find the diameter of B roll of copper wire?
Simple, don't think too complicated

When the diameter of N copper wires is equal to the diameter of Y copper wires, substituting 0.8y/n, the diameter of copper wires can be obtained without a ruler. Or because the diameter of copper wires is known, the cross-sectional product s can be obtained. According to the formula r = P * L / s, the cross-sectional product s can be obtained

As shown in the figure, the ball with mass m is suspended at the top of the semicircular smooth track with mass m, and the indication of the platform scale is (M + m) g. ignoring the delay factor of the platform scale, the indication of the platform scale is ()
A. Always less than (M + m) GB. Always greater than (M + m) GC. First less than (M + m) g and then greater than (M + m) Gd. First greater than (M + m) g and then less than (M + m) g

When the ball is just released, the acceleration is g, and there is no elasticity to m, so the reading of the platform scale is equal to Mg, less than (M + m) g; the ball is only subject to gravity in the process of movement, and the mechanical energy is conserved, as follows: Mgr = 12mv2 & nbsp; at the lowest point, the resultant force of gravity and supporting force provides centripetal force, according to Newton's second law, as follows: n-mg = mv2r & nbsp; & nbsp; ② The simultaneous solution: n = 3mg, so the platform scale reading is (M + 3M) g, greater than (M + m) g; so C

How much buoyancy do you have when you float on alcohol? How much buoyancy do you have when you put it on water
The 28 in one machine is a 200cm3 solid copper block placed in water. What is the buoyancy n (copper = 8.9 * 10 cubic kg / m3
Come on

1. Because floating, so g = 800 cattle, so it's 800 cattle on the water
V row = f floating divided by (g * alcohol density) = 800N divided by (10 * 0.8 * 1000) = 0.1m3
2. Because of immersion
So V row = V material = 200 cm3
F floating = density of water * g * V row = 1000 * 10 * 200 * 0.000001 = 2n

1. There are three incandescent lamps, a PZ 220 V 15, B PZ 220 V 40, C PZ 220 V 100. They are connected in parallel in the home circuit. Which of them is the brightest? Why?
2. Connect two small bulbs in parallel to the power supply, close the switch and find that L1 is brighter than L2. Why?

C high rated power
One is less than two

In convex lens imaging, u is less than f, is it between F and 2F or after 2F
What's the difference between u and 2F?

When u is less than f, it becomes a vertical magnified virtual image, and the image distance is greater than the object distance (V & gt; U)
In any area, as shown in the figure below:

With people's increasing awareness of environmental protection, water-saving sanitary ware has gradually entered people's families. The so-called water-saving sanitary ware refers to the sanitary ware whose water consumption is less than 6L each time. Xiaomin's family has newly installed a set of water-saving sanitary ware whose water consumption is 5L each time, Q: (1) how many times can 1000 kg of water be used for washing this water-saving sanitary ware? (2) how many tons of water can Xiaomin's house save every month (10 times a day on average, 30 days a month)?

1000 kg of water can be used for 200 times
1.2t water saving per month
N = m / M = 1000 / (5 × 1) = 200 times
The original monthly water use
m1=10×30×9×1=2700kg=2.7t
Monthly water consumption after water saving
m2=10×30×5×1=1500kg=1.5t
Water saving = m1-m2 = 1.2t

1 kg / m3=__ G / cm3; 1 g / cm3=_ Kg / m3
2. Density of water: what is the density of water_ The physical meaning of it is________________ .
3. Unit conversion: the mass of chlorine is (1) 1.7 * 10 ^ - 27kg= Gram= (2) the mass of the moon is about 7.4 * 10 ^ 25g=_ Tons=_ Kilogram= Mg
4. (1) the quality of a junior high school student is about 45_ (2) The mass of an elephant is about 5.8_ (3) The weight of a chicken is about 2.0 * 10 ^ 6_ .
5. The mass of a piece of iron is 5kg. If it is rolled into iron plate, the mass is 5kg If you take it to the moon, what's its mass_ If it is completely melted into molten iron in a furnace, its mass is_ .
6. The mass of a piece of iron is 1.97 tons, the volume is 0.25 cubic meters, and the density of iron is_ Kg / m3, combined_ G / cubic centimeter; if half of the iron block is cut off, the density of the iron block is_ .
7. After a piece of 1 m ^ 3 ice melts into water, its mass is , volume_____ .
8. The mass of a hollow aluminum ball is 27g. After the hollow part is filled with alcohol, its total mass is 48g (P alcohol = 0.8 * 10 ^ 3kg / m ^ 3, p aluminum = 2.7 * 10 ^ 3kg / m ^ 3). Calculate the volume of the aluminum ball

1.1, 12.1.0 * 10 ^ 3kg / m3, the mass of water per kilogram is 1000kg, 3.1.7 * 10 ^ 24g = 1.7 * 10-30t4.kg, t, g5.5kg, 5kg, 5kg6.7.88 * 10 ^ 3kg / m3, 7.88g/cm3, 7.88 * 10 ^ 3kg / m37.1000kg, 1m38. V aluminum = m / P = 27g / 2.7 * 10 ^ 3kg / m3 = 0.027kg/2.7 * 10 ^ 3kg / m

What is the main function of periscope in military_____________________________ .