第 10 类 RD Sharma 解决方案 - 第 16 章表面积和体积 - 练习 16.1 |设置 1
问题 1. 一个半径为 8 厘米的实心铅球可以制成多少个半径为 1 厘米的球?
解决方案:
R = 8 cm
r = 1 cm
Let the number of balls = n
Volume of the sphere = 4/3 πr3
The volume of the solid sphere = sum of the volumes of n spherical balls.
n x 4/3 πr3 = 4/3 πR3
n x 4/3 π(1)3 = 4/3 π(8)3
n = 83 = 512
Therefore, 512 balls can be made of radius 1 cm each with a solid sphere of radius 8 cm.
问题 2. 从 11dm x 1 mx 5 dm 的矩形金属块中可以铸造多少个直径为 5 cm 的球形子弹?
解决方案:
A metallic block of dimension 11dm x 1m x 5dm
Diameter of each bullet = 5 cm
Volume of the sphere = 4/3 πr3
1 dm = 0.1 m
The volume of the rectangular block = 1.1 x 1 x 0.5 = 0.55 m3
Radius of the bullet = 5/2 = 2.5 cm = 0.025cm
Let the number of bullets = n.
The volume of the rectangular block = sum of the volumes of the n spherical bullets
0.55 = n x 4/3 π(0.025)3
n = 8400
Therefore, 8400 can be cast from the rectangular block of metal.
问题 3. 将一个半径为 3 厘米的球体熔化并重铸成三个球体。其中两个球的半径分别为2厘米和1.5厘米。确定第三个球的直径?
解决方案:
Radius of the spherical ball = 3 cm
Volume (V) = 4/3 π33
Ball is melted and recast into 3 spherical balls.
Volume (V1) of first ball = 4/3 π 1.53
Volume (V2) of second ball = 4/3 π23
Let the radius of the third ball = r cm
Volume of third ball (V3) = 4/3 πr3
V = V1 + V2 + V3
4/3 π33 = 4/3 π 1.53 + 4/3 π23 +4/3 πr3
On Solving
33 = 1.53 + 23 + r3
27 = 3.375 + 8 + r3
r3 = 15.625
r= 2.5
d = 2×r
= 5cm
问题 4. 将 2.2 立方 dm 的黄铜拉成直径 0.25 cm 的圆柱线。找出电线的长度?
解决方案:
Radius of the wire (r) = d/2
= 0.25/2 =
= 0.125cm
1dm = 10cm
2.2 dm = 22cm
Let the length of the wire be (h)
Volume of the cylinder = πr2h
Volume of cylindrical wire = Volume of brass
πr2h = 22
(22/7)*(0.125)2h = 22
h = 7/(0.125)2
h = 448
Therefore, the length of the cylindrical wire drawn is 448 m
问题 5. 将直径为 2 厘米的实心圆柱体重铸成长度为 16 厘米、外径为 20 厘米、厚度为 2.5 毫米的空心圆柱体必须取多长?
解决方案:
Diameter of the solid cylinder = 2 cm
Length of hollow cylinder = 16 cm
Volume of a cylinder = πr2h
Radius of the solid cylinder = 1 cm
Volume of the solid cylinder = π12h = πh cm3
Volume of the hollow cylinder = πh(R2– r2)
Thickness of the cylinder = (R – r)
0.25 = 10 – r
Internal radius of the cylinder = 9.75 cm
Volume of the hollow cylinder = π × 16 (102-9.752) [ (a2-b2) = (a+b)(a-b)]
= π × 16 (10+9.75)(10-9.75)
= 16π(19.75)(0.25)
Volume of the solid cylinder = volume of the hollow cylinder
πh = 16π(19.75)(0.25)
h = 79cm
Therefore, the length of the solid cylinder = 79.04 cm.
问题 6. 一个直径等于其高度的圆柱形容器装满水,将水倒入两个完全装满的直径为 42 厘米、高度为 21 厘米的相同圆柱形容器中。求圆柱形容器的直径?
解决方案:
The diameter of the cylinder = the height of the cylinder
⇒ h = 2r
Volume of a cylinder = πr2h
Volume of the cylindrical vessel = πr22r = 2πr3 (as h = 2r)….. (i)
Diameter = 42 cm, so the radius = 21 cm
Height = 21 cm
Volume of two identical vessels = 2 x π 212 × 21 ….. (ii)
Volumes on equation (i) and (ii) are equal
2πr3= 2 x π 212 × 21
r3 = (21)3
r = 21 cm
d = 42 cm
Therefore, the diameter of the cylindrical vessel is 42 cm.
问题 7. 将 50 个直径为 14 厘米、厚度为 0.5 厘米的圆板叠放在一起,形成一个正圆柱体。求它的总表面积。
解决方案:
Radius of circular plates = 7cm
Thickness of plates = 0.5 cm
Total thickness of all the plates = 0.5 x 50 = 25 cm (height of cylinder)
Total surface area of the right circular cylinder formed = 2πr × h + 2πr2
= 2πr (h + r)
= 2(22/7) x 7 x (25 + 7)
= 2 x 22 x 32 = 1408 cm2
Therefore, the total surface area of the cylinder is 1408 cm2
问题 8. 将 25 个圆板,每块半径为 10.5 厘米,厚度为 1.6 厘米,叠放在一起,形成一个实心圆柱体。求这样形成的圆柱的曲面面积和体积。
解决方案:
Total height = 1.6 x 25 = 40 cm
Curved surface area of a cylinder = 2πrh
= 2π × 10.5 × 40
= 2640 cm2
Volume of the cylinder = πr2h
= π × 10.52 × 40
= 13860 cm3
Therefore, curved surface area of the cylinder = 2640 cm2 and the volume of the cylinder = 13860 cm3
问题 9. 找出底部直径为 1.5 厘米、高度为 0.2 厘米的金属圆盘的数量,将其熔化成一个高 10 厘米、直径 4.5 厘米的直圆柱体。
解决方案:
Radius of each circular disc = r = 1.5/2 = 0.75 cm
Height of each circular disc = h = 0.2 cm
Radius of cylinder = R = 4.5/ 2 = 2.25 cm
Height of cylinder = H = 10 cm
Let the number of metallic discs required is given by n
n = Volume of cylinder / volume of each circular disc
n = πR2H/ πr2h
n = (2.25)2(10)/ (0.75)2(0.2)
n = 3 x 3 x 50 = 450
Therefore, 450 metallic discs are required.
问题 10. 可以从尺寸为 66 cm × 42 cm × 21 cm 的实心矩形铅块中获得多少个直径为 4.2 cm 的球形铅弹。
解决方案:
Radius of each spherical lead shot = r = 4.2/ 2 = 2.1 cm
The dimensions of the rectangular lead piece = 66 cm x 42 cm x 21 cm
Volume of a spherical lead shot = 4/3 πr3
= 4/3 x 22/7 x 2.13
Volume of the rectangular lead piece = 66 x 42 x 21
The number of spherical lead shots = Volume of rectangular lead piece/ Volume of a spherical lead shot
= 66 x 42 x 21/ (4/3 x 22/7 x 2.13)
= 1500
Therefore, number of spherical lead shots = 1500
问题 11. 一个边长为 44 厘米的实心立方体铅可以制成多少直径为 4 厘米的球形铅丸。
解决方案:
The radius of each spherical lead shot = r = 4/2 = 2 cm
Volume of each spherical lead shot = 4/3 πr3 = 4/3 π 23 cm3
Edge of the cube = 44 cm
Volume of the cube = 443 cm3
Number of spherical lead shots = Volume of cube/ Volume of each spherical lead shot
= 44 x 44 x 44/ (4/3 π 23)
= 2541
问题 12. 将三个边缘比例为 3:4:5 的金属立方体熔化并转化为对角线为 12√3 厘米的单个立方体。找到三个立方体的边缘。
解决方案:
Let the edges of three cubes be 3x, 4x and 5x respectively.
Volume of the cube after melting will be = (3x)3 + (4x)3 + (5x)3
= 27x3 + 64x3 + 125x3
= 216x3
Let a be the edge of the new cube so formed after melting
a3 = 216x3
a = 6x
Diagonal of the cube = √(a2 + a2 + a2) = a√3
12√3 = a√3
a = 12 cm
x = 12/6 = 2
Therefore, the edges of the three cubes are 6 cm, 8 cm and 10 cm respectively.
问题 13. 一个半径为 10.5 厘米的固体金属球被熔化并重铸成许多较小的圆锥体,每个圆锥体的半径为 3.5 厘米,高度为 3 厘米。找出这样形成的圆锥的数量。
解决方案:
Radius of metallic sphere = R = 10.5 cm
Volume = 4/3 πR3 = 4/3 π(10.5)3
Radius of each cone = r = 3.5 cm
Height of each cone = h = 3 cm
Volume = 1/3 πr2h = 1/3 π(3.5)2(3)
The number of cones = Volume of metallic sphere/ Volume of each cone
= 4/3 π(10.5)3 / 1/3 π(3.5)2(3)
= 126
问题 14. 金属球的直径等于 9 厘米。将其熔化并拉制成直径为 2 毫米、横截面均匀的长线材。找出电线的长度。
解决方案:
Radius of the sphere = 9/2 cm
Volume = 4/3 πr3 = 4/3 π(9/2)3
Radius of the wire = 1 mm = 0.1 cm
Let the length of the wire = h cm
Volume of wire = πr2h = π(0.1)2h
Volume of wire = Volume of sphere
π(0.1)2h = 4/3 π(9/2)3
h = 4 x 729/ (3 x 8 x 0.01) = 12150 cm
Therefore, the length of the wire = 12150 cm
问题 15. 一个铁球被熔化并重铸成相同大小的小球。如果每个小球的半径是原球半径的1/4,那么这样的球有多少?比较所有小球的表面积与原始球的表面积。
解决方案:
Let the radius of the big ball be x cm
Radius of the small ball = x/4 cm
Let the number of balls = n
Volume of n small balls = Volume of the big ball
n x 4/3 π(x/4)3 = 4/3 πx3
n x (x3/ 64) = x3
n = 64
Therefore, the number of small balls = 64
Surface area of all small balls/ surface area of big ball = 64 x 4π(x/4)2/ 4π(x)2
= 64/16 = 4/1
Therefore, the ratio of the surface area of the small balls to that of the original ball is 4:1
问题 16. 将一个半径为 3 厘米的铜球熔化并重铸成一个高 3 厘米的正圆锥体。求圆锥底的半径?
解决方案:
Radius of the copper sphere = 3 cm
Volume of the sphere = 4/3 π r3
= 4/3 π × 33 ….. (i)
Height of the cone = 3 cm
Volume of the right circular cone = 1/3 π r2h
= 1/3 π × r2 × 3 ….. (ii)
(i) and (ii) are equal
4/3 π × 33 = 1/3 π × r2 × 3
r2 = 36
r = 6 cm
Therefore, the radius of the base of the cone is 6 cm.
问题 17. 一根直径为 1 cm、长度为 8 cm 的铜棒被拉成一根长度为 18 m、厚度均匀的导线。求线的粗细?
解决方案:
Diameter of the copper rod = 1 cm
Radius of the copper wire = 1/2 cm = 0.5 cm
Length of the copper rod = 8 cm
Volume of the cylinder = π r2h
= π × 0.52 × 8 ……. (i)
Length of the wire = 18 m = 1800 cm
Volume of the wire = π r2h
= π r2 × 1800 ….. (ii)
(i) and (ii) are equal
π × 0.52 × 8 = π r2 × 1800
r2 = 2 /1800 = 1/900
r = 1/30 cm
Therefore, the diameter of the wire is 1/15 cm = 0.67 mm
问题 18. 空心球壳的内、外表面直径分别为 10 厘米和 6 厘米。如果将其熔化并重铸成一个长度为 8/3 的实心圆柱体,求圆柱体的直径?
解决方案:
Internal diameter of the hollow sphere = 6 cm
Internal radius of the hollow sphere = 6/2 cm = 3 cm = r
External diameter of the hollow sphere = 10 cm
External radius of the hollow sphere = 10/2 cm = 5 cm = R
Volume of the hollow spherical shell = 4/3 π × (R3 – r3)
= 4/3 π × (53 – 33) ….. (i)
Let the radius of the solid cylinder be r cm
Volume of the cylinder = π × r2 × h
= π × r2 × 8/3 ….. (ii)
(i) and (ii) are equal
4/3 π × (53 – 33) = π × r2 × 8/3
4/3 x (125 – 27) = r2 × 8/3
98/2 = r2
r2 = 49
r = 7
d = 7 x 2 = 14 cm
Therefore, the diameter of the cylinder is 14 cm