The problem of the circumference of a circle is urgent 1. A 20 meter long rope is used to encircle a tree trunk for six times, leaving 1.16 meters. How many meters is the diameter of the tree trunk, 2. A yong road is 47.1 meters long. Xiao Ming rolls an iron ring on the Yong road. The diameter of the iron ring is 30 cm. How many turns does the iron ring have to turn when rolling from one end of the Yong road to the other The problem of Yonglu, the unit is different, the formula calculation, I just that, missed the word, now most need the second problem

The problem of the circumference of a circle is urgent 1. A 20 meter long rope is used to encircle a tree trunk for six times, leaving 1.16 meters. How many meters is the diameter of the tree trunk, 2. A yong road is 47.1 meters long. Xiao Ming rolls an iron ring on the Yong road. The diameter of the iron ring is 30 cm. How many turns does the iron ring have to turn when rolling from one end of the Yong road to the other The problem of Yonglu, the unit is different, the formula calculation, I just that, missed the word, now most need the second problem

Circumference of circle = Π * diameter
1: Trunk circumference: (20-1.16) / 6 = 3.14m
Diameter on trunk = 3.14 / Π = 1m
2: The iron ring turns for one turn, Π * 30 / 100 = 0.3 Π M
The number of rings to turn: 47.1 / 0.3 Π = 50
The hoop needs to turn 50 times

On the circumference of a circle
1. The minute hand of a wall clock is 15 cm long. After 15 minutes, what is the distance of the minute hand tip? 60 minutes?
2. After three-quarters of an hour, the tip of a clock's minute hand just goes 94.2 cm. How long is the minute hand?
3. The length of the minute hand of a wall clock is 1.5 times the length of the hour hand. The tip of the minute hand of an hour just goes 37.68 cm. How many cm does the hour hand go?
Why, how to calculate, what's the reason? The good is increasing the reward score by 20. The better, the more

The minute hand of a wall clock is 15 cm long. After 15 minutes, what is the distance of the needle tip? 60 minutes?
Distance = 2 π × 15 × 15 △ 60 = 23.55cm, 60 minute distance = 2 π × 15 = 94.2cm
2. After three-quarters of an hour, the tip of a clock's minute hand just goes 94.2 cm. How long is the minute hand?
Three fourths of an hour is three fourths of a circle
So there are
The length of minute needle = 94.2 △ (2 π × 3 / 4) = 20cm
3. The length of the minute hand of a wall clock is 1.5 times the length of the hour hand. The tip of the minute hand of an hour just goes 37.68 cm. How many cm does the hour hand go?
Length of minute needle = 37.68 △ 2 △ 3.14 = 6cm
The length of the hour hand = 6 △ 1.5 = 4cm
So the hour hand is about 4 × 2 π × 1 / 12 = 2.09cm

As shown in the figure, the radius of the bottom area of the cone r = 10cm, and the length of the generatrix
As shown in the figure, the radius of the bottom area of the cone is 10 cm, and the length of the generatrix is 40 cm

If the side of the cone is expanded along the generatrix SA, the length of arc AA 'is 2 π r = 20 π, SA = 40, so 20 π = n π· 40 / 180, so n = 90 ° so the center angle of the side expansion of the cone is 90 ° s surface = s side + s bottom = 90 π· 40 / 360 + π· 10 = 500 π (CM)

If the side area of the cone is twice the area of the bottom, what is the central angle of the cone side development?

180
According to the first sentence, we can make the following equation: 2pir ^ 2 = 1 / 2 * L * 2pi * r
Where R is the radius of the bottom and l is the length of the generatrix
The result is: l = 2R
According to the formula of perimeter of fan open area, L * @ = 2R * @ = (perimeter of bottom surface) 2pi * r
(the circumferential arc length of the fan shaped by expanding the side face is the circumference of the original bottom face)
So we can get the angle @ = pi = 180

The generatrix length of a cone is 15, the center angle of the side expanded view is 2 π / 3, and the side area and volume of a sphere are 2 π / 3

S=2π15*15/3=2*3.14*15*15\3=471
L=2dπ/3=2πD
D=d\3=15\3=5
H*H=15*15-D*D=200
H=15*15-5*5=14.14
V=D*DπH\3=5*5*3.14*14.14\3=370

If the side area of a cone is 15 π / 4 and the length of generatrix is 3, then the center angle of the expanded side view is?

(15π/4)/(π*3^2)*2*π=5/6π

If the side area of the cone is 10 π cm ^ 2 and the center angle of the expanded side area is 36 degrees, then the generatrix length of the cone is?
The process

Its side view is fan-shaped
Conical generatrix is sector radius
R²=S÷（nπ/360°）
R²=10π×（360°/36°π）
R²=100
R1 = 10, R2 = - 10 (not rounding off)
The length of conical bus is 10cm

If a sector with radius of 3cm and central angle of 120 ° is used to form the side of a cone, then the bottom radius of the cone is

One centimeter

What is the radius of the ground circle of a cone if there is a fan-shaped piece of paper with a radius of 8 and a center angle of 90 degrees, which just encloses the side of the cone?

The bottom radius of the cone is 2cm
The reasons are as follows.
The sector arc length is 2 π * 8 / 4 = 4 π
That is, the perimeter of the bottom surface
4π=2πR
So r = 2

There is a fan-shaped paper with a center angle of 90 ° and a radius of 8cm, which is used to form the side of a cone
The radius of the circle at the bottom of the cone is several centimeters

For what, volume?
1/3*S*h
Bottom area s
S=pi*[(l/pi)/2]^2
=pi*[1/4*pi*16/pi/2]^2
=4*pi
Bottom radius r = 2
H = (radical) sqrt (R ^ 2-r ^ 2)
=sqrt(64-4)=sqrt(60)
V=1/3*4pi*sqrt(60)
=8sqrt(15)/3*pi