E - Density and Pressure

Question 1

A block of copper has a volume of 10cm3 and a mass of 90g. Calculate its density.

Answer 1

ρ = m/Vρ = 90/10ρ = 0.09kg / 0.00001m3ρ = 9000 kg/m3

Question 2

Aluminium has a density of 2700 kg/m3. Calculate the volume of a 4kg block.

Answer 2

ρ = m/VV = m/ρV = 4/2700V = 0.00148 m3

Question 3

What is 1m³ in cm³?

Answer 3

1000000 cm3.

Question 4

What is 1 litre in cm³?

Answer 4

1000 cm³

Question 5

What is 1 litre in m³?

Answer 5

0.001 m³

Question 6

density, mass and volume

Answer 6

density = mass/volume

Question 7

A correct unit for density is

Answer 7

g/cm³ or kg/m³

Question 8

What measuring instrument would you use to measure volume?

Answer 8

measuring cylinder

Question 9

what measuring instrument would you use to measure mass?

Answer 9

electronic balance or electronic scales

Question 10

How should you use an electronic balance to make as accurate measurement as possible?

Answer 10

1. Set it to zero first
2. Place on a flat level surface

Question 11

How could a student make the measurement form a measuring cylinder as accurate as possible?

Answer 11

1. Place eyes level with the water.
2. Place on a flat surface
3. Use a clean cylinder

Question 12

A student wants to measures the density of water.

State two factors that she should keep the same throughout her experiment.

Explain why.

Answer 12

1. The temperature of water should be kept constant as hot water is less dense.
2. The water should be of the same type, for example water with salt in it could be more dense.

Question 13

How do Inuits stop themselves sinking into the snow?

Answer 13

The weight is spread over a larger area.

This means that there is less force per unit area acting on the surface and therefore the surface can support the object better.

Question 14

Why shouldn’t you walk on wooden floors in pointy high heels?

Answer 14

The weight is spread over a small area. This means that there is a lot of force per unit area acting on the surface and therefore the floor will get damaged.

Question 15

What is the formula for pressure?

Answer 15

pressure = force /area

P - pressure in pascals (Pa)

F - force in newtons (N)

A - area in m2

Question 16

A 70kg man has shoes with an area of 200 cm2. Calculate the pressure exerted on the floor by the man.

Answer 16

35000 Pa

Question 17

The 70kg man puts on stilts (they have a mass of 5 kg). The area is now reduced to an area of 20 cm2. Calculate the new pressure exerted on the floor by the man.

Answer 17

375000 Pa

Question 18

A canister of gas has a pressure of 200000 Pa. The internal surface area is 200 cm2. Calculate the force exerted on the interior surfaces of the canister by the gas.

Answer 18

4000N

Question 19

What is the formula for pressure at a depth?

Answer 19

pressure = density x g x depth

P = ρgh

Question 20

A chamber is submerged so that its top is 3m below the surface of a freshwater lake. The canister is 4m in height. Calculate the difference in pressure between the top and bottom of the canister:

Answer 20

For the top: P = 1000 x 10 x 3= 30000Pa

For the bottom:P = 1000 x 10 x 7= 70000Pa

The difference is therefore 70000 - 30000 = 40000 Pa

Question 21

A water tower is filled to a depth of 6m. Calculate the pressure of the water at the bottom of the container.

Answer 21

P = ρgh

P = 1000 x 10 x 6

= 60000Pa

The density of water is 1000