Port Said International Schools
Better education for future generations
Science Department
Grade: 7
Worksheet 1
Work sheet 1 Answers
1) Give reason for each of the following:
1- Balloons filled with hydrogen or helium rise up in the air.
Because hydrogen and helium have less density than air.
2- A piece of iron sinks in water but cork floats.
Iron has more density than water, so it sinks.
Cork has less density than water, so it floats.
3- Water is not used in extinguishing petrol fires.
Because petrol oil has less density than water, so it floats above water, so it
cannot be extinguished by water.
4- Ice changes into water after a period of time.
Because ice has low melting point.
2) Choose the correct answer:
1- Matter is anything that has ……………………
( mass and volume)
2- If you know that the density of water is 1 g/cm3, so the volume of 10 gm of
water is…………………
( 10 cm3)
3- The density of helium is ……………………………….. that of air.
( less than)
4- The color property is a distinguishing factor between………….……….
(iron and gold)
5- The smell property is a distinguishing factor between……………
(perfume and vinegar )
6- The taste property is a distinguishing factor between………………………
(milk and honey)
3) Problems:
1- When a piece of iron of mass 78 g is put in a graduated cylinder containing
100 cm 3 of water, the reading of the cylinder becomes 110 cm3, calculate the
density of iron.
The volume of iron = 110 – 100 = 10 cm3
𝑀𝑎𝑠𝑠
Density = 𝑉𝑜𝑙𝑢𝑚𝑒
=
78
10
= 7.8 gm /cm3
Port Said International Schools
Better education for future generations
Science Department
Grade: 7
Worksheet 1
2- Calculate the density of a cube, its mass is 70 g and its volume is 9 cm3.
Density =
𝑀𝑎𝑠𝑠
𝑉𝑜𝑙𝑢𝑚𝑒
=
70
9
gm/cm3
3- In an experiment for determination the density, the mass of the used beaker
(empty) was 25 g, the mass of the beaker (containing liquid) was 75 g.
Calculate the density of the liquid if its volume is 50 cm3.
Mass of liquid = 75- 25 = 50 gm
Density =
𝑀𝑎𝑠𝑠
𝑉𝑜𝑙𝑢𝑚𝑒
=
50
50
= 1 gm/cm3
4- A piece of metal has a mass of 189 g, volume of 3 cm3. Calculate its density.
Density =
𝑀𝑎𝑠𝑠
𝑉𝑜𝑙𝑢𝑚𝑒
=
189
3
= 63 gm/cm3
4) Choose from (A) that is suitable to (b):
A
B
1- The measuring unit of density.
- gram.
2
2- The measuring unit of mass.
- Cm.
4
3- The measuring unit of volume.
- Cm3.
3
4- The measuring unit of length.
- g / cm3.
1
5) Complete the following:
1- Unit of volume is cm3 and that of mass is kg or kg or gram.
2- Density is mass unit volume of the substances and its unit is gm/cm3.
3- Melting point is the temperature at which matter changes from solid into
liquid.
4- Materials that have less density than water float on it,
but materials that have more density than water sink in it.