Answer:
B) A stack of books is carried at waist level across a room
Explanation:
Work is defined as:
where
F is the force applied
d is the displacement of the object
is the angle between the direction of the force and of the displacement
From the formula, we see that the work done is zero when the force and the displacement are perpendicular to each other. Let's now analyze each situation:
A) A bookcase is slid across carpeting. --> work is done, because the force that pushes the bookcase is in the same direction of the displacement
B) A stack of books is carried at waist level across a room. --> no work is done, because the force to carry the book is vertical, while the displacement of the books is horizontal
C) A chair is lifted vertically with respect to the floor. --> work is done, because the force that lifts the chair is vertical, and the displacement is vertical as well
D) A table is dropped onto the ground. --> work is done, because the force of gravity (that makes the table falling down) is vertical and the displacement of the table is also vertical.
The total amount of energy always stays the same because of the law of conservation of energy, meaning that there is always the same amount of energy, it just gets turned into different forms like potential energy, kinetic energy, sound, thermal, etc.
243000, take the 4,860 and times it by 50
1. Avogadro's hypothesis. Avogadro hypothesized that equal volumes of all gases (at the same pressure) will have the same number of molecules. From PV=nRT, we know that one mole of gas takes up 22.4 L
2. Mass number. The mass number is the sum of the protons and neutrons in the nucleus so Carbon 12 has an atomic number of 6 which indicates 6 protons, and a mass number of 12 so 12-6 = 6 neutrons.
3. Avogadro's number. Avogadro's number is the number of units in one mole of any substance, which has been defined as 6.02 x10^23
4. Isotopes are the different forms of a single element. They differ in neutrons. One example is Hydrogen which has three isotopes Protium, Deuterium, and Tritium.
5. Atomic mass. The mass of the atom is equal to the sum of the protons and the neutrons as electrons are so small their mass is negligible. This is not exactly the same as the mass number because this number takes into account the different isotopes
6. mole A mole has the same number of entities as 12 grams of carbon 12, it is expressed by Avogadro's number so 1 mole = 6.02 x10^23 atoms or molecules, etc
7. molar mass- the amount that one mole of substance weighs. For carbon 12, 12 grams has one mole of atoms by definition. So for carbon 12, the molar mass is 12 g/mol
Answer:
A friend snorkeling just below the surface of the water along the same shore will detect the sound first.
Explanation:
- The speed of sound in water medium is faster than that through the air.
- Sound propagates through the medium by transferring through the molecules on it. Water has more closely packed molecules due to which the speed is faster.
- In fact, the sound's speed in water is almost four times faster than that in the air.
- So the guy in the water surface gets to hear sound faster than the one in sore.
