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N.B. The questions for the SAT subject physics test.
Heat is added to a 2.0-kg block of ice. The specific heat of water is 4.2 x 10^3 J/Kg'C and the heat of fusion of ice is 3.3 x 10^5 KJ/Kg.
1. How much heat is required to melt the block of ice?
(A) 1.2 x 10^4 J
(B) 6.5 x 10^4 J
(C) 1.7 x 10^5 J
(D) 6.6 x 10^5 J
(E) 8.4 x 10^5 J
2. Once the ice melts, heat is added until the temperature of the water reaches 30'C. How much heat is required to raise the the temperature from 0'C to 30'C?
(A) 8.4 x 10^4 J
(B) 2.5 x 10^5 J
(C) 3.0 x 10^5 J
(D) 6.0 x 10^5 J
(E) 1.9 x 10^6 J
1. Newton's First Law of Motion
Three fundamental principles, called Newton's First, Second and Third Laws, form the basis of classical, or Newtonian, mechanics and have proved valid for all mechanical problems not involving speeds comparable with the speed of light and not involving atomic or subatomic particles. Newton's First Law states that a particle not subjected to external forces remains at rest or moves with constant speed in a straight line. This is also known as the Law of Inertia.
Newton's first law of motion is often stated as: An object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force.
2. Newton's Second Law of Motion
The second law is the one that tells you how to calculate the value of a force. Force (measured in Newtons) is one of the fundamental physical properties of a system and comes in many forms. You might feel it as a push or pull (a mechanical force), while it is the value of your weight (the gravitational force of the Earth pulling on you) and can be seen in the repulsion or attraction of magnets or electric charges (electromagnetic force).
The Law is often stated as: The acceleration of a particle is directly proportional to the resultant external force acting on the particle and is inversely proportional to the mass of the particle, or a = F/m.
3. Newton's Third Law of Motion
If two particles (or bodies) interact, the force exerted by the first particle on the second particle (called the action force) is equal in magnitude and opposite in direction to the force exerted by the second particle (called the reaction force).
Suppose you are watching the lift off of a rocket, like the ones by SpaceX. You hear a deafening roar and see burning gases shooting from the exhaust vents of the rockets. At that moment, the rocket moves slowly upward. You can infer that the force for the lift off comes from the burning gases pushing against the shuttle rockets. Why does the shuttle system move in the opposite direction of the gases?
The forces on the rocket are similar to the forces in a collision between two tennis balls. When the balls collide, they are propelled in opposite directions. The rockets force burning gases downward through the exhaust vents. In response to these downward forces, the shuttle system moves upward. The motion of the rocket demonstrates Newton's third law of motion. When one object exerts a force upon a second object, the second object exerts an equal and opposite force upon the first object.
The third law of motion states that every action has an equal and opposite reaction. You can see equal and opposite forces interact when you blow up a balloon and release it, it moves in the opposite direction. The force propelling the balloon is equal and opposite to the force of the air leaving the balloon.
4. Newton's Law of Universal Gravitation
Newton's Law of Universal Gravitation states that a particle attracts every other particle in the universe using a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between their centers.
5. Einstein's Special Theory of Relativity
Einstein's theory about the relationship between space and time is based on two postulates: (1) that the laws of physics are invariant in all inertial systems and (2) that the speed of light in a vacuum is the same for all observers, regardless of the motion of the light source.
6. Zeroth Law of Thermodynamics
The principle states that if two bodies are each in thermal equilibrium with a third body, then the first two bodies are in thermal equilibrium with each other.
7. First Law of Thermodynamics
The First Law of Thermodynamics states that heat is a form of energy, and thermodynamic processes are therefore subject to the principle of conservation of energy. This means that heat energy cannot be created or destroyed. It can, however, be transferred from one location to another and converted to and from other forms of energy.
8. Second Law of Thermodynamics
The Second Law of Thermodynamics is commonly known as the Law of Increased Entropy. While quantity remains the same (First Law), the quality of matter/energy deteriorates gradually over time. How so? Usable energy is inevitably used for productivity, growth and repair. In the process, usable energy is converted into unusable energy. Thus, usable energy is irretrievably lost in the form of unusable energy.
"Entropy" is defined as a measure of unusable energy within a closed or isolated system (the universe for example). As usable energy decreases and unusable energy increases, "entropy" increases. Entropy is also a gauge of randomness or chaos within a closed system. As usable energy is irretrievably lost, disorganization, randomness and chaos increase.
We can imagine thermodynamic processes which conserve energy but which never occur in nature. For example, if we bring a hot object into contact with a cold object, we observe that the hot object cools down and the cold object heats up until an equilibrium is reached. The transfer of heat goes from the hot object to the cold object. We can imagine a system, however, in which the heat is instead transferred from the cold object to the hot object, and such a system does not violate the first law of thermodynamics. The cold object gets colder and the hot object gets hotter, but energy is conserved. Obviously we don't encounter such a system in nature and to explain this and similar observations, thermodynamicists proposed a second law of thermodynamics. Clasius, Kelvin, and Carnot proposed various forms of the second law to describe the particular physics problem that each was studying.
The second law states that there exists a useful state variable called entropy S. The change in entropy delta S is equal to the heat transfer delta Q divided by the temperature T.
delta S = delta Q / T
9. Third Law of Thermodynamics
The Third Law of Thermodynamics is concerned with the limiting behavior of systems as the temperature approaches absolute zero. Most thermodynamics calculations use only entropy differences, so the zero point of the entropy scale is often not important. However, we discuss the Third Law for purposes of completeness because it describes the condition of zero entropy.
The Third Law states, “The entropy of a perfect crystal is zero when the temperature of the crystal is equal to absolute zero (0 K).” According to Purdue University, “The crystal must be perfect, or else there will be some inherent disorder. It also must be at 0 K; otherwise there will be thermal motion within the crystal, which leads to disorder.”
While a temperature of absolute zero does not exist in nature, and we cannot achieve it in the laboratory, the concept of absolute zero is critical for calculations involving temperature and entropy. Many measurements imply a relationship to some starting point. When we state a distance, we have to ask, distance from what? When we state a time, we have to ask, time since when? Defining the zero value on the temperature scale gives meaning to positive values on that scale. When a temperature is stated as 100 K, it means that the temperature is 100 K above absolute zero, which is twice as far above absolute zero as 50 K and half as far as 200 K.
10. Law of Conservation of Mass-Energy
The principle that energy cannot be created or destroyed, although it can be changed from one form to another. After Einstein announced E = mc^2 equation, this law was developed to combine the Law of Conservation of Mass formulated by Antoine Lavoisier in 1785 with the Second Law of Thermodynamics (the Law of Conservation of Energy).
11. Law of Conservation of Momentum
The Law of Conservation of Momentum states that the momentum will remain constant no matter what until and unless any external force comes into action. For a collision occurring between object X and object Y in an isolated system, the momentum lost by object X is equal to the momentum gained by object Y.
12. Coulomb's Law
Coulomb's Law describes the electrostatic interaction between electrically charged particles. The law states that the force between two point charges acts in the direction of the line between them and is directly proportional to the product of their electric charges divided by the square of the distance between them. The law is analogous to Isaac Newton's inverse-square Law of Universal Gravitation.
13. Gauss's Law
Gauss's Law, also known as the Gauss's Flux Theorem, is a law relating the distribution of electric charge to the resulting electric field. The law states that the net flux of an electric field through a closed surface is proportional to the enclosed electric charge. It is one of Maxwell's four equations that form the basis of classical electrodynamics.
14. Ohm's Law
Ohm's Law describes the relationship among current, resistance and voltage. The law states that resistance is directly proportional to voltage and indirectly proportional to current.
15. Quantum Mechanics
Most of physics study phenomena about the atomic level. Quantum mechanics studies the sub-atomic. You need to know the photoelectric effect, atomic models to describe the structure of atoms, nuclear stability and decay, binding energy and nuclear reactions like fission and fusion.
An astronomer discovers a planet with two moons. One moon is 2 times as far from the center of the planet as the other and 3 times the mass of the other moon. What is the ratio of the gravitational force on the first moon to the gravitational force on the second moon?
A 1-newton force and a 4-newton force act in opposite directions. What is the magnitude of the resultant force, in newtons?
An object starts from rest and accelerates at 6.0 m/s^2 for 4.0 seconds. How far does it travel?
(A) 8.0 m
(B) 12 m
(C) 48 m
(D) 96 m
(E) 288 m
Force A and Force B act on an object. Let theta equal the angle between the directions of the two forces. At what value of theta is the resultant force the greatest?
(A) 0 deg
(B) 45 deg
(C) 60 deg
(D) 90 deg
(E) 180 deg
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