Physics Unit 2
What is the relationship between liquid pressure and the depth of a liquid?
Pressure in a liquid depends onthe depth (shown by h), and the density of the liquid (D).
What happens to the pressure in all parts of a confined fluid in a container if the pressure in one part is increased?
According to the Pascal's Principle this "extra pressure" will be transmitted through theentire fluid. Therefore, in every part of the fluid as well as the can, this extra pressure willshow up.
What the first Kepler's law of planetary motion
First Kepler's law is related to the orbit of the planets around the sun. It statesthat the orbits are elliptical
How much heat is needed to raise the temperature of 70 grams of water from 20 C to 80 C?
First we calculate the needed heat for ONE gram of water. For every degreeincrease, we need 1 calorie. For 60 degrees (i.e. 80 - 20 = 60), we need 60 calories per gram of water. But we have 70 grams. The answer is 4200 cal of heat
When does the force of gravity become large enough that we can see or feel it?
In order for the force of gravity to become significantly large, at least one of theobjects must have an extremely large mass.
A merchant in Kathmandu sells you a solid-gold 1-kg statue for a very reasonable price. When you return home, you wonder whether or not you got a bargain. So youlower the statue into a container and measure the volume of displaced water. Whatvolume will verify that it is pure gold?
You need the density of gold which is 19.3 kg/m^3. You use this to calculate the volume. Final answer: 51.8 cm ^3
The force of gravity acting on an object of mass m located on the surface of the moon ia 1/6th of the force of gravity when the object is on the earth's surface. Explain
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If 200 cal of heat are added to a system, how much energy has been added in joules?
1 cal=4.18 J. Convert to 836 J
What is the mass of 1 liter of water? What is its weight?
Mass= 1 kg Weight 9.8 N
In Australia which is located in the southern hemisphere, the official winter seasonstarts on June 22 and the summer starts on December 22. In which case the earth iscloser to the sun?
when the summer starts in thesouthern hemisphere, the earth is closer to the sun. Of course at this time, the winter startsin the northern hemisphere. As it is explained in the computer review lesson, the tilt of the earth axis is such that during our winter, the tilt points away from the sun, creatingless direct sunshine, etc.
What is the definition of momentum?
1.The quantity of motion of a moving body, measured as a product of its mass and velocity
How does the force of gravity between two objects change when the distance between them is doubled
1/4 the inital force. A factor of "4" in the denominator of the force equation causes the force to become smaller by a factor of 4.
A 2-kg box is sliding down an inclined surface. At some point, its speed is 4 m/s.What is its kinetic energy?
16 J
The second floor of a house is 6 m above street level. How much work is required tolift a 300-kg piano to the second-floor level?
17640 J
The depth of water behind the Hoover Dam is 220 m. What is the water pressure atthe base of this dam?
2,156,000 pa
For the woman of the previous question, what happens to her weight if the earth'smass remains the same, but the earth radius is halved?
2000 N
A 1-gram piece of iron of specific heat of 0.11 is at the temperature 20 C. If we add 1 calorie of heat to the iron, what is its final temperature?
29.1 C. For every 0.11 calorie, the heat goes up by one degree. 1/0.11=9.1. 20 C + 9.1=29.1
If all bodies apply an attractive force of gravity to each other, why don't we seeobjects around us being attracted toward each other?
Answer: The force of gravity is the weakest force in the nature. The gravitationalconstant "G" has a value which is extremely small. Its value in the metric system is G= 6.67 x 10 ^-11 . This makes the force between "ordinary" objects like people, cars, balls, etc. to be so small (but not zero) that is practically undetectable.
Where do you weigh more - at the earth poles or on the earth equator?
At the earth poles
What is "calorie" and what is its definition?
Calorie is a unit for heat. Heat is a form of energy and can be specified in"joules". However, due to historical reasons, calorie is normally used in conjunction with heat. One calorie is the amount of heat (energy) to change the temperature of one gram of water by 1 degree Celsius.
The temperature on a warm summer day is 95 F What is this temperature indegrees Celsius and in Kelvin (absolute) scale?
Celsius: 35 Kelvin:308
Heat is added to a container of water is which is in state of boiling. What happens tothe water temperature?
During the phase change, that is when water (a liquid) turns into steam, thetemperature remains unchanged in spite of the fact that heat is added to the water.
What is the law of universal gravitation?
Every body in the universe attracts other bodies with a force that is directly proportional to product of their masses, and inversely proportional to the square of the distance between them: F= G (m1) (m2)/r^2
Give an example when your weight is less than "mg".
For the astronauts inside the space station
How does the force of gravity between two objects change when the distance betweenthem is halved
Force becomes larger by a factor of 4.
How does the force of gravity between two objects change when the distance between them is tripled
Force becomes smaller by a factor of 9
Distinguish between pressure and force.
Force is a push or pull action between objects. Pressure is force acting on a surface area of an object, thus it is force per unit area.
What are the temperatures for freezing water and boiling water on the Celsius andFahrenheit scales?
Freezing point is at 0 C which is the same as 32 F. Boiling point of water is at 100C which is the same as 212 F
Distinguish between temperature and heat.
Heat is a form of energy. It is the internal energy (i.e. the sum of all molecular energy within a system like a container of water) which is transferred from one object toanother due to their temperature difference. Temperature is NOT a form of energy. The average kinetic energy of all molecules in asystem is a MEASURE of the temperature of that system. In other words, temperature is proportional to the average kinetic energy of all molecules.
What impulse occurs when an average force of 10 N acts on a cart for 2.5 s?
Impulse = force x time of contact Impulse = (10 N) x (2.5 s) = 25 N.s
What is the unit of energy in SI (i.e. metric) system?
Joules
What is the difference between kinetic energy and (gravitational) potential energy
Kinetic energy is energy associated with motion. When a car is in motion, it possesses kinetic energy. Therefore, for an object to have kinetic energy, its velocity must be non zero. Potential energy is the energy associated with position. When a piece of rock is lifted to acertain height, it possesses potential energy. When a climber climbs a mountain, his potential energy is increasing.
Suppose you are at the bottom of a dry well of depth 5 m. How much initial kineticenergy would you have to give to a 0.5-kg stone when throwing it for it to just reachthe top of the well?
Let's assume the depth of 5 m is from where the stone is thrown to the top of thewell. At the bottom, the stone has zero potential energy, but some kinetic energy as youthrow it upward. At the top, the stone has zero kinetic energy but some potential energy.Since the total energy at the top must be the same as the bottom, we can write, 24.5 J
What is the difference between work and power?
Power is related to work and energy. By definition, power is the amount of work (or energy) done in one second. Therefore, a 1200 watt space heater provides 1200 joulesof thermal energy per second.
How does the water pressure one meter below the surface of a small pond comparewith water pressure one meter below the surface of a huge lake?
They are he same because the density of both water sources in the same.
When a moving car comes to a stop on a level road, what happens to its kineticenergy?
Most of the energy is dissipated due to friction and appears as thermal energy inthe brakes, tires, and the ground.
What is a neap tide?
Neap tides are especially weak tides. They occur when the gravitational forces of the Moon and the Sun are perpendicular to one another (with respect to the Earth). Neap tides occur during quarter moons.
In a glass of water at room temperature, do all the molecules have the same speed?
No, they have a range of speeds, but th eaverage is what is calculated
The astronauts inside the space station are usually shown to be "floating". Does thatmean that they are weightless?
No. There is still the force of gravity acting on them.
A woman weighs 500 N on the surface of the earth. If the earth's mass were todouble, what would happen to her weight?
So she would weigh 1000 N.
What is specific heat?
Specific heat is the amount of heat to change the temperature of 1 gram of anysubstance by 1 degree Celsius. The equation is cal/grams-degree celsius
What is a spring tide?
Spring tides are especially strong tides (they do not have anything to do with the season Spring). They occur when the Earth, the Sun, and the Moon are in a line. The gravitational forces of the Moon and the Sun both contribute to the tides. Spring tides occur during the full moon and the new moon.
What is the acceleration of gravity "g" at the location of the astronaut of the previousquestion?
The acceleration of gravity also behaves as inverse square law Answer = 1.1 m/s ^2
A 900-N astronaut has climbed a ladder as shown in the figure. Each step of theladder is equal to the radius of the earth. What is the weight of the astronaut in thelocation shown?
The astronaut has a force of gravity of 900 N at the surface of the earth. At thelocation shown, he is 3 times the earth's radius from the center of the earth. In other words, he has increased his distance from earth (as measured from the center) by a factor of 3. The force of gravity of him is going to decrease by a factor of 9. His weight is now 100 N
Why does a bimetallic strip bend with changes in temperature?
The bimetallic strip is made up of two metals with different expansion(compression) rate. When heated, the metal with the high expansion rate expands morethan the metal with the low expansion rate.
For the same force, why do long cannon impart more speed to a cannonball thansmall cannon?
The forces are the same but the long cannon impart a larger impulse. For thelong cannon, the cannonball is acted upon by the same force for a longer period of timethan the small cannon. This causes the ball to accelerate at a higher rate and end up with ahigher velocity.
A large piece of tree trunk has a smaller density than a small steel ball. How couldthis be?
The large piece of tree trunk has a large mass. But it also has alarge volume. The density is the ratio of the two which becomes less for wood (treetrunk) than iron (steel ball).
Why is it called a "universal" law?
The law of gravity applies to all masses in the universe. In other words, nomatter where the objects are located in the universe, the force of gravity between themfollows the same "universal" law, as stated by the law of gravity.
At which of the positions does the planet in elliptical orbit experiences a greater (a)gravitational force, (b) speed, (c) acceleration?
The position that is closes to the sun
How can one explain the Kepler's second law using the law of gravity?
The second law is the law of areas. When the planet is closer to the sun, itexperiences a greater force of gravity than when it is farther from the sun. This makes the planet to travel at a faster speed at the closer distance than at a farther distance from thesun. This is consistent with the law of areas.
Which produces a bigger tidal effect on the earth - the sun or the moon?
The sun applies a significantly larger gravitational force on the earth then themoon. However, the tidal effects not only depend on the strength of the force, but also onthe force difference on each side of the earth. Since the sun's distance from the earth isvery large, the difference between the forces on each side is much less significant than the forces on the same side due to the moon. This makes the moon produce tidal effectsthat are about 50% more significant than the sun's tidal effects.
What is the relationship between force and momentum?
There is a direct relationship between force and momentum. The rate at which momentum changes with time is equal to the net force applied to an object.
Why do both the sun and the moon exert a greater gravitational force on one side of the earth than the other?
This is due to the law of gravity. The side of the earth that is "closer" to the sunor the moon will experience a greater force of attraction then the other side which isfarther.
A 6-kg piece of metal displaces 1 liter of water when submerged. What is its density?
Use d=m/v= 6 g/cm ^3
Which has a higher specific heat, water or sand?
Water has a higher specific heat and because of that, it takes longer to warm andof course, longer to cool.
Does a substance that cools off quickly have a high or low specific heat?
When an object cools off quickly, it indicates that it has a small specific heat.
If a 1-L container is immersed halfway into water, what is the volume of water displaced? What is the buoyant force acting on the container?
When the container is immersed halfway into water, it displaces water equal toits volume into the water. This means that 0.5 L of water is displaced.The buoyant force is the weight of the displaced fluid. First we calculate mass and thenweight, exactly as it is done in the previous question. Answer: 4.9 N.
A swimmer dives from atop of a flagpole into a swimming pool below. His potentialenergy at the top is 10000 J. What is his kinetic energy when his potential energyreduces to 1000 J?
When the potential energy is reduced to 1000 J, his kinetic energy must be 9000 J.
When you touch a cold surface, does cold travel from the surface to your hand or does energy travel from your hand to the cold surface?
When you touch the surface, thermal energy is transferred from your hand(high temperature system) to the cold surface (low temperature system). This is basicallythe definition of "heat", which is the transfer of internal energy due to temperaturedifference. The direction of heat transfer is always from the higher temperature to thelower temperature.
If you swim beneath the surface in salt water, will the pressure be greater than infreshwater at the same depth?
Yes, because the density of salt water is greater than the density of fresh water.
Can we use "joules" as a unit for heat?
Yes.
What do we call the gravitational force between the earth and your body?
Your Weight
Where do you weigh more - at the bottom of Death Valley or atop one of the peaks of the Sierra Nevada?
Your weight is the force of gravity, and it depends on your distance from the"center" of the earth. At the bottom of the Death Valley, you have a shorter distance tothe center than on peak of the Sierra Nevada. Therefore, you weigh more on the DeathValley then on the peak of the Sierra Nevada.
A box is pulled across a flat floor with a net force of 15 N which is directed parallelto the floor. The box starts at rest and is pulled for 5 seconds causing it to travel adistance of 4 meters. (a) How much work is done on the box? (b) How much is thekinetic energy of the box after it travels 5 m? (c) How much power is used during thismotion?
a- 60 J b- 60 J c- 12 watts
When is your weight equal to mg?
at the surface of the earth
Name four "forms" of energy.
mechanical,thermal,chemical,electromagnetic,electrical,and nuclear
What is the value of atmospheric pressure near the sea level?
p=1000pa or 1 atm=760 mm hg
Two cylinders, one filled with oxygen and one filled with hydrogen gas, are at thesame temperature. Which gas molecules have a higher average speed?
themolecules with the larger mass will have a smaller speed in order to end up with the samekinetic energy. In this case, oxygen molecules have larger mass than hydrogen molecules.Thus the oxygen molecules will have a smaller average speed than the hydrogenmolecules.
