In order to judge whether an iron ball is hollow or not, the density of iron is 7.9g/cm3, the mass of iron ball is 79, and the volume of water is 60.0 The total volume of water and iron balls is 75.0 1. Is the ball hollow or solid 2. If the ball is hollow, what is the volume of the hollow part

In order to judge whether an iron ball is hollow or not, the density of iron is 7.9g/cm3, the mass of iron ball is 79, and the volume of water is 60.0 The total volume of water and iron balls is 75.0 1. Is the ball hollow or solid 2. If the ball is hollow, what is the volume of the hollow part

The iron ball is hollow
（1）：
According to the formula volume = mass / density
=79g/7.9g/cm^3
=10cm^3
V iron + V water = 10cm ^ 3 + 60cm ^ 3 = 70cm ^ 3 < 75cm ^ 3
So the iron ball is hollow!
（2）：
V hollow = V iron (hollow) - V iron (solid)
=75cm^3-60cm^3-10cm^3
=5cm^3
So the hollow part is 5cm ^ 3

The density of physical iron is 7900kg / m3, the mass of an iron ball is 39.5, and the volume is 10
The density of iron is 7900kg / m3, the mass of an iron ball is 39.5kg, and the volume is 10dm3
The unit should be changed to kg / m

Hello ~ this topic uses the hypothetical method ~ assuming that the iron ball is solid ~ then we can calculate the volume of 39.5kg solid iron ball ~ V = mass / density = 39.5kg divided by 7900kg / m3 = 0.005m3 = 5dm3, and the topic tells you that the volume is 10dm35dm3 < 10dm3, that is, the volume of a solid iron ball is only

Immediately the first mock exam is to calculate the conversion of physical units. For example, the density of kilograms is equal to the number of grams per cubic meter per cubic centimeter.

Junior high school physics unit and unit conversion
1、 Mechanical unit
1、 Length (L), distance (s) international unit: meter (m)
Common units: kilometer (km), decimeter (DM), centimeter (CM), millimeter (mm)
μ m, NM
Light year: a unit of length, the distance light travels in a year
1km =
1X103m
1dm=0.1m=1x10-1 m
1cm=0.01m=1x10-2m
1mm=0.001m=1x10-3m
1цm=1x10-6 m
1nm=1x10-9m
Decimal: 1m 10 1dm 10
1cm 10
1mm
100 carry: 1 m 102
1cm
1dm 102 1mm
Thousand carry: 1km 103 1m 103
1mm 103 1цm
103 1nm
2、 Area (s) SI unit square meter (M2)
Area formula: S = ab
Common units: square decimeter DM2, square centimeter cm2, square millimeter mm2
1 dm2=1x10-2 m2
1c m2=1 x 10-3 m2
1 mm2=1 x 10-6 m2
Hundred carry: 1 m2 102 1
dm2 102 1 c
m2 102 1 mm2
3、 Volume unit international unit cubic meter (M3)
Volume formula: v = sh
Common units: cubic decimeter DM3, cubic centimeter (cm3), milliliter (ML), liter (L)
1ml= 1cm3= 1 x 10-6m3
1l = 1dm3= 1 x10-3 m3
Thousand carry: 1m3 103 1dm3 (1L)
103 1cm3（1ml）
3、 Time (T) Si (s)
Common units: hour (H), minute (min)
1h=3600s 1min=60s
4、 Velocity (V) SI unit meter per second (M / s)
1m/s= 3.6km/h
5、 Mass (m) SI unit: kilogram (kg)
Common units: ton (T), gram (g), milligram (mg)
1t=1 x 103kg 1g=1 x
10-3kg 1mg=1 x
10-6kg
Kilocarry: 1t 103 1kg
103 1g
103 1mg
6、 Density (ρ) in kg / m3
Common unit: g / cm3
1 x103 kg/m3 = 1 g/cm3-
ρ water = 1 g / cm3 = 1 X103 kg / m3
7、 Force (f)
SI unit Newton (n)
The formula is: g = m, g = 9.8n/kg or 10N / kg
8、 Pressure (P) SI unit: Pascal (PA)
Liquid pressure formula: P = ρ GH
Note: only applicable to liquid or cylindrical solid (cuboid, cube, cylinder),
Generally, the pressure P = ρ GH and then the pressure f = PS are calculated
Solid pressure formula: P = f / S
Note: it is applicable to the pressure of all objects. For the pressure and pressure of solids, generally, the pressure f = g is calculated first, and then the pressure (cylindrical liquid pressure f = g liquid))
1 Pa=1N/ m2
Common unit: kPa, 1kPa = 1x103pa
9、 Work (W)
International unit: Joule (J) 1J = 1n. M
10、 Power (P)
W / S = 1 W (International Unit)
Common unit: kw
1kw=1 x 103w
[mechanics department]
[Formula]
1. Speed: v = s / T
2. Gravity: g = mg
3. Density: ρ = m / V
4. Pressure: P = f / S
5. Liquid pressure: P = ρ GH
6. Buoyancy:
(1) , f floating = f lower - f upper
(pressure difference)
(2) F = G-F (apparent gravity)
(3) F = g
(floating, floating)
(4) Archimedes principle: F floating = g row = ρ liquid GV row
7. Lever balance condition: F1. L1 = F2
L2
8. Ideal slope: F / g = H / L
9. Ideal pulley: F = g / n
10. Actual pulley: F = (G + G) / n
(lifting heavy objects vertically)
11. Work: w = FS = GH
(lifting objects up)
12. Power: P = w / T = FV
13. Principle of work: W hand = w machine
14. Actual machine: wtotal = w + W extra
15. Mechanical efficiency:
η = w yes / W total
16. Pulley block efficiency:
(1) , η = g / NF (vertical direction)
(2) , η = g / (G + G) (vertical direction without friction)
(3) , η = f / NF (horizontal direction)
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