Question

1. would 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:

1. Work is calculated by the formula $W = Fd$ (force times distance). Lifting a box from the floor to above your head involves a greater distance than lifting it to the top of a table. So, more work is done lifting it to above your head.
2. A rock thrown at the glass has kinetic energy due to its motion. Kinetic energy can cause more damage than the rock sitting still (which has only potential energy relative to the glass). So, the thrown - rock is more likely to break the glass.

10.
a. Earbuds convert electrical energy into sound energy. Main energy: electrical energy.
b. A match before it is struck has chemical potential energy stored in its chemicals. Main energy: chemical potential energy.
c. The LED on a DVD player display emits light, converting electrical energy into light energy. Main energy: electrical energy.
d. A battery stores chemical potential energy that can be converted into electrical energy. Main energy: chemical potential energy.
e. A stove burner converts electrical or chemical (if gas - powered) energy into heat energy. Main energy: heat energy.
f. A power plant that uses uranium for fuel converts nuclear energy into electrical energy. Main energy: nuclear energy.

1. The identity of an atom is determined by the number of protons in its nucleus. When an uncharged atom becomes an ion, it gains or loses electrons, but the number of protons remains the same. So, the identity of the atom does not change.
2. A compound is considered 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.
3. Molecules of an element are made up of only one type of atom, while molecules of a compound are made up of two or more different types of atoms chemically bonded together.
4. Nuclear changes such as nuclear fission or fusion can produce an atom different from the original one. In nuclear reactions, the number of protons in the nucleus can change, thus changing the identity of the atom.

Answer:

1. More work is done lifting the box from the floor to above your head because the distance of the lift is greater.
2. The rock thrown at the glass is more likely to break it because it has kinetic energy.

10.
a. Electrical energy
b. Chemical potential energy
c. Electrical energy
d. Chemical potential energy
e. Heat energy
f. Nuclear energy

1. No, because the number of protons (which determines the identity) remains the same when an atom becomes an ion.
2. It has a fixed composition and distinct chemical properties.
3. Molecules of an element consist of one type of atom, while molecules of a compound consist of different types of atoms.
4. Nuclear changes.