A circle has a radius of 2m and an area of π*r*r=4π. A rectangle has a length equal to the circumference of the circle and a width of 2π*r=4π.
Is equal to the diameter of a circle =2r=4, the area of a rectangle = length times width =4π*2r= 16π,
The area difference is 16π-4π= 12π.
(2) The length of the second hand is 1cm. How many centimeters will the tip of the second hand go in 2 hours?
Second,
The length of the second hand is 1 cm, which is equivalent to the radius of 1 cm. The needle tip of the second hand takes 2 hours =2*60 minutes, and the second hand rotates once per minute. * * * Go 120 laps *2π*r=240π cm.
(3) The radius of the train driving wheel is 0.75m.. If it rotates 300 times per minute, how many kilometers does the train travel per hour?
Third,
The radius of the driving wheel of the train is 0.75m, and its circumference is 2π * r = 1 .5π m. If it rotates 300 times per minute and1hour equals 60 minutes, then 300 times *60* circumference = 300 * 1.5π = 24000π Mi Yue equals 7540.
(4) A certain type of washbasin produced by enamel factory is made of circular iron sheet with a diameter of 0.5m.. If 800 washbasins are produced every day, how many iron sheets do you need? Four, a circular iron sheet with a diameter of 0.5 meters, a radius of 0.25 meters and an area of π*r*r=0.625*π square meters, then 800 pots need at least 800*0.625*π square meters = 1570.8 square meters if the waste loss is not calculated.
(5) A lead is 62.8 cm long. If you enclose it in two circles of equal size, what is the area enclosed by this lead?
5. Lead wire is 62.8 cm long. If two circles of equal size are enclosed, the length of the lead wire should be the sum of the perimeters of the two circles, 62.8=2* (the circumference of the circle) =2*2*π*r, and π is 3. 14. Then, the value of R radius is 5 cm, and the areas of two circles are the same, which are both π *.
6. The hour hand length of the wall clock is10cm. How many centimeters did it walk after a day and a night at the top of the hour hand?
Walk twice a day and night.
Walking distance: 2 * 2 π r = 2 * 2 * 3.14 *10 =125.6cm.
7. Xiaogang used a 452.6-decimeter-long rope to wrap around the trunk for six times. What is the circumference of this box? What is the area of the cross section in square centimeters?
The circumference of this tree is: 452.6÷6≈75.4 decimeters.
Radius: 75.4(3. 14 * 2)≈ 12 decimeter.
The cross-sectional area is: 3. 14* 12? =452. 16 square decimeter
8. It takes 3.768 meters for a thread to wrap around a cylindrical mouth three times. What is the area of this cylinder mouth?
The circumference of this cylinder mouth is: 3.768 ÷ 3 =1.256 m.
The radius is:1.256÷ (3.14 * 2) = 0.2m.
Area: 3. 14*0.2? = 0.0628 m2
9. The hour hand length of the wall clock is10cm. 12 hours later, what is the area swept by this hour hand?
/kloc-walked around in 0/2 hour.
The swept area is: πr? =3. 14* 10? = 3 14cm2
10, the bottom of a wooden basin is round, and a 2.552-meter-long iron wire is tied to its bottom, and the joint of the iron wire is 0.04 meters. What is the diameter of the bottom of this wooden basin?
The circumference of the bottom of this wooden basin is: 2.552-0.04 = 2.512m.
Diameter: 2.512 ÷ 3.14 = 0.8m.
1 1, the length of an iron hoop is 1 1.49 decimeter, which is just a hoop of a barrel. It is known that the joint of the iron hoop is 5 cm. What is the outside diameter of this barrel?
The outer circumference of the barrel is:11.49-0.5 =10.99 decimeter.
Diameter: 10.99÷3. 14=3.5 decimeter.