KCL Section 1: Fluids & density and pressure (Materials)

Question 1

What are fluids?

Give examples

Answer 1

Fluids can flow.

Liquids and gases are both fluids.

Question 2

Write down the SI units for: density, mass, volume, pressure, force, area, weight

Answer 2

kgm^-3
kg
m^3
Nm^-2
N
m^2
kgms^-2

Question 3

Write down the formula to calculate the area of a circle and the volume of a sphere

Answer 3

pi * r^2

4/3 * pi * r^3

Question 4

A house brick is 23 cm long. 10 cm wide and 7 cm high, its mass is 3.38kg.
What is the brick’s density?

Answer 4

2100 kgm^-3

Question 5

At 20 degrees celsius, a child’s balloon filled with helium is a sphere with a radius of 20 cm. The mass of helium in the balloon is 6 grams.
What is the density of helium at this temperature?

Answer 5

0.1791044776 kgm^-3

Question 6

The mass of 20 steel ball bearings is 42g. Their mean diameter is 8.0mm.

What is the density of one ball bearing?

Answer 6

The volume of one ball bearing = 4/3 * π * r^3 = 4/3 * π(4 * 10^-3)^3 = 2.68 * 10^-7
The mass of one ball bearing = 42 * 10^-3 / 20 = 2.1 * 10^-3

(2. 110^-3)
- —————– = 7.8 x 10^3
(2. 6810^-7)

7.8 x 10^3 kgm^3

Question 7

Calculate the density of a solid cube with sides 5.0 cm and mass 1.31kg.

Answer 7

10500 kgm^-3

Question 8

Calculate the mass of 150 m of copper cable of circular cross section with diameter 0.5mm. The density of copper is 8.9 gcm^-3.

Answer 8

262g

0.262kg

Question 9

Calculate the volume of mercury in a container if the total mass is 5.5kg and an empty container has mass 0.45kg.
The density of mercury is 13.6 x 10^-3

Answer 9

0.00037 m^3

Question 10

Aerogel question

Answer 10

0.15%

Question 11

1 kg of nitrogen is used to fill a balloon. The density of nitrogen is 1.25 kgm-3; what is the volume of the balloon?

Answer 11

0.8 m^3

Question 12

What will be the mass of air in a classroom that is 15 m long, 10 m wide and 4 m high? (Density of air = 1.3 kgm-3)

Answer 12

780 kg

Question 13

A tank measures 60 cm long and 45 cm wide. If 72 kg of water is enough to fill the tank, how deep is the tank? (Density of water = 1000 kgm-3).

Answer 13

0.3 m

Question 14

A solid of steel cylinder has a diameter of 12 mm and a length of 85 mm . Calculate:
(A) its volume in m3.
(B) and its mass in kg, density of steel = 7800 kgm-3.

Answer 14

A. 9.6 x 10^-6 m^3

B. 0.075 kg

Question 15

The density of the air = 1.2 kgm^-3
The density of water = 1.0 x 10^3 kgm^3

A spherical bubble of air, radius 2.0 mm, under water has what volume?

Answer 15

3.35 x 10^-8 m^3

Question 16

The density of the air = 1.2 kgm^-3
The density of water = 1.0 x 10^3 kgm^3

A spherical bubble of air, radius 2.0 mm, under water has what is the weight?

Answer 16

3.9 x 10^-7 N

Question 17

true or false

The SI unit for energy can be expressed as kgm^2s^-1

1 kg m^-3 = 0.001 g cm^-3

The volume of a sphere can be calculated using πr2

Volume = density/mass

1000 cm3 = 1 m3

ρ = density

Volume of a cylinder = πr2L

1 mg = 0.0000001 kg

Answer 17

F
F
F
F
T
T
T

Question 18

Derive an expression for weight which includes density.

Answer 18

gfs * ρ * v

Question 19

A cube with sides of 25cm has a weight of 4.67 N. What is the density of the material?

Answer 19

30.5

Question 20

pressure = force / area

Air pressure is about 100kPa. On one centimeter this is a force of:

Answer 20

10N