Question

1. should you do more work lifting a box from the floor to the top of a table or from the floor to a shelf above your head? why? 9. which will probably break a pane of glass, a small rock sitting on the glass or the same rock thrown at the glass? why? 10. state the main kind of energy associated with the following sources. a. earbuds b. a match before it is struck c. the led on a dvd player display d. a battery e. a stove burner f. a power - plant that uses uranium for fuel 11. does the identity of an uncharged atom change when it becomes an ion? explain. 12. why is a compound considered a pure substance? 13. what is the difference between the molecules of an element and the molecules of a compound? 14. which changes in matter can produce an atom different from the original?

Explanation:

Step1: Analyze work - lifting box

Work is calculated as $W = Fd$ (force times distance). Lifting a box to a shelf above your head has a greater distance $d$ compared to lifting it to a table. Assuming the force $F$ (equal to the weight of the box $mg$) is the same, more work is done when lifting it to the higher shelf.

Step2: Analyze rock - breaking glass

A rock thrown at glass has kinetic energy $K=\frac{1}{2}mv^{2}$. A sitting rock has only potential energy due to its position. The moving rock has more energy to transfer to the glass upon impact, so it is more likely to break the glass.

Step3: Identify energy types

a. Earbuds convert electrical energy to sound energy, but the main stored energy is electrical.
b. A match before it is struck has chemical potential energy.
c. The LED on a DVD - player display emits light, so the main energy is light (electromagnetic) energy.
d. A battery stores chemical energy.
e. A stove burner emits heat, so the main energy is thermal energy.
f. A uranium - powered power plant uses nuclear energy.

Step4: Analyze atom identity - ion formation

The identity of an atom is determined by the number of protons (atomic number). When an uncharged atom becomes an ion, only the number of electrons changes, not the number of protons. So the identity of the atom does not change.

Step5: Explain compound as pure substance

A compound is a pure substance because it has a fixed composition and distinct chemical properties. It is made up of two or more elements chemically combined in a definite ratio.

Step6: Differentiate element and compound molecules

Molecules of an element consist of only one type of atom, while molecules of a compound consist of two or more different types of atoms chemically bonded together.

Step7: Identify matter changes for atom change

Nuclear changes (such as nuclear fission, nuclear fusion, and radioactive decay) can change the number of protons in an atom, thus producing an atom different from the original. Chemical changes only involve the rearrangement of electrons and do not change the identity of the atom.

Answer:

1. You do more work lifting a box from the floor to a shelf above your head because work $W = Fd$ and the distance $d$ is greater. The thrown rock is more likely to break the glass because it has kinetic energy while the sitting rock only has potential energy.
2. a. Electrical energy; b. Chemical potential energy; c. Light (electromagnetic) energy; d. Chemical energy; e. Thermal energy; f. Nuclear energy.
3. No, because the identity of an atom is determined by the number of protons and ion - formation only changes the number of electrons.
4. A compound is a pure substance because it has a fixed composition and distinct chemical properties.
5. Molecules of an element have only one type of atom, while molecules of a compound have two or more different types of atoms.
6. Nuclear changes (nuclear fission, nuclear fusion, radioactive decay) can produce an atom different from the original.