Science Homework 5

Questions 1 and 2 are based on the following information.

Energy is needed to break the bonds between the atoms within molecules

and the bonds that exist between molecules. The energy required to break

these bonds can vary depending on the types of bonds involved and the

types of elements involved. The chart shows the melting points for

substances A, B, C, and D

Which substance contains the strongest bonds?

• A

• B

• C

• D

Answer explanation

Substance D, with the highest melting point, will need the most average kinetic energy (temperature) to break its bonds. Therefore, substance D on the table has the strongest bonds.

Questions 1 and 2 are based on the following information.

Energy is needed to break the bonds between the atoms within molecules

and the bonds that exist between molecules. The energy required to break

these bonds can vary depending on the types of bonds involved and the

types of elements involved. The chart shows the melting points for

substances A, B, C, and D

Substance A is most likely made of which type(s) of elements?

• metals

• a metal and a nonmetal

• nonmetals

• a semimetal and a nonmetal

Answer explanation

Substances made of all nonmetals will have lower melting points. For example, wax is made up of elements that are nonmetals. That is why a wax candle melts easily with a small flame. In contrast, iron, which is all metal, needs a blow torch to melt it.

Questions 3–6 refer to the following information.

Matter is anything that occupies space and has mass. Matter can be a solid

such as steel, a liquid such as water, or a gas such as air. Elements are pure

substances composed of only one type of atom. An atom is the smallest

particle of an element that has the properties of the element.

Neutral atoms have a charge of zero. If an atom gains electrons, it

becomes negatively charged, and if an atom loses electrons, it becomes

positively charged. Once an atom has an electrical charge, it is called an

ion. The number of protons never changes in an atom and is unique for

every element.

Which of the following has a positive charge?

• Proton

• Neutron

• Atom

• Electron

Answer explanation

Protons have a positive charge.

Electrons have a negative charge.

Neutrons does not have charge.

Questions 3–6 refer to the following information.

Matter is anything that occupies space and has mass. Matter can be a solid

such as steel, a liquid such as water, or a gas such as air. Elements are pure

substances composed of only one type of atom. An atom is the smallest

particle of an element that has the properties of the element.

Neutral atoms have a charge of zero. If an atom gains electrons, it

becomes negatively charged, and if an atom loses electrons, it becomes

positively charged. Once an atom has an electrical charge, it is called an

ion. The number of protons never changes in an atom and is unique for

every element.

The subatomic particle that distinguishes one element from another is a(n)...

• Proton

• Neutron

• Ion

• Electron

Answer explanation

The number of protons distinguishes one element from

another.

Questions 3–6 refer to the following information.

Matter is anything that occupies space and has mass. Matter can be a solid

such as steel, a liquid such as water, or a gas such as air. Elements are pure

substances composed of only one type of atom. An atom is the smallest

particle of an element that has the properties of the element.

Neutral atoms have a charge of zero. If an atom gains electrons, it

becomes negatively charged, and if an atom loses electrons, it becomes

positively charged. Once an atom has an electrical charge, it is called an

ion. The number of protons never changes in an atom and is unique for

every element.

Magnesium has 12 protons and electrons. When charged, it loses 2 electrons. Which symbol represents the charged magnesium (Mg) ion?

• Mg^2-

• Mg

• Mg²⁺

• Mg^-

Answer explanation

Calculate the charge on the ion:

Neutral magnesium has 12 protons: 12 + and 12 electrons: 12−, so the charge was 0 initially; after magnesium loses two electrons, the total number of electrons becomes 10−.

Therefore, the net charge = (12+) − (10−) = 2+; Mg2+.

Questions 3–6 refer to the following information.

Matter is anything that occupies space and has mass. Matter can be a solid

such as steel, a liquid such as water, or a gas such as air. Elements are pure

substances composed of only one type of atom. An atom is the smallest

particle of an element that has the properties of the element.

Neutral atoms have a charge of zero. If an atom gains electrons, it

becomes negatively charged, and if an atom loses electrons, it becomes

positively charged. Once an atom has an electrical charge, it is called an

ion. The number of protons never changes in an atom and is unique for

every element.

In a neutral atom, the number of _________ equals to the number of________

Answer explanation

In a neutral atom, the numbers of protons and

electrons are equal.

Newton’s first law of motion states that an object continues to be in a state

of rest or motion unless it is acted on by an external force. The net force

acting on the body is the total of all the forces acting on the body. Newton’s

first law is sometimes called the law of inertia, which is the tendency of an

object to resist changes in velocity. Inertia of an object is directly

proportional to its mass.

A book is placed on a dashboard of a car that is stopped at a traffic

light. As the car starts to move forward, the book slides off the

dashboard. Pick the most correct explanation for the book sliding off

the dashboard.

• There is grease on the dashboard, so the book slides off the

  dashboard.

• Due to inertia, the book slides off the dashboard.

• The book is heavy, so it slides off the dashboard.

• Air resistance made the book move backward.

Answer explanation

Inertia is the book's resistance to a change in its state of motion. The book remained at rest and did not move forward with the car.

A soccer ball weighing 500 g is lying near the center line of the field.

A player kicks it with a force of 400 N. What is the velocity of the

ball after 5 seconds?

• 4000 m/s

• 3200 m/s

• 1600 m/s

• 800 m/s

Answer explanation

a = F/m and a = v/t

F/m = v/t , v = (400 N/0.5 kg) × 5 s = 4,000 m/s

A driver accelerates his car first at a rate of 1.8 m/s2 and then at a rate

of 1.2 m/s2. What will be the ratio of the two forces exerted by the

engine at the two rates?

• 1 : 2

• 2 : 1

• 2 : 3

• 3 : 2

Answer explanation

The mass of the cars does not change, so F1 = m × 1.8 m/s2 and F2

= m × 1.2 m/s2.

F1/F2 = 3:2

If the net force acting on a sliding block is tripled, the acceleration

will increase by ___________ times.

Answer explanation

Since acceleration is directly proportional to the net force

applied to an object, if the net force is tripled, the acceleration will be tripled.