Physics Final exam
Consider a 100 kg Father and his 20 kg girl. They decide to enjoy balancing on a seesaw, which is a uniform board 4 m long and pivoted exactly at its center. If girl sits at the seesaw's end (2m from the center), how far from the center on the other side should the father sit?
0.4m
A ball hits a wall going 10 m/s, and bounces off going 7 m/s. The coefficient of restitution is:
0.70
Suppose the earth's polar ice caps melted, sending water towards the equator and increasing the moment of inertia of the earth to 1.1 times its present value. The angular velocity of the earth will be
0.909 times its present value
What mass has a rest energy of 100J?
1.1x10-15 kg
Imagine that you are able to go on a fishing trip that you have always wanted to. Your friend gets a bite that exerts a force of about 50N on the pole and it bends by a certain amount. Now you have a pole identical to your friends and you get a hit that bends the pole about twice as much. You can estimate that the force on your pole is about:
100N
A tricycle releases 56 J of gravitational potential energy while rolling 0.523 m directly downhill along a ramp. What is the downhill force (if constant) acting on the tricycle?
107.07N
Atmospheric pressure is about 100000 Pa. At what depth in water does this pressure double?
10m
If you double the absolute temperature of a star, its power output increases by a factor of _______.
16
An ideally efficient freezer cools food to 210K. If room temperature is 300K, and the machine consumes 75 J of work, how much heat was removed from the food?
175J
If you double the radiating surface area of a star, its power output increases by a factor of _______.
2
A gymnast jumps upward with an initial speed of 10 m/s. She is in the air for a total time of about
2 seconds
An elevator releases 10400 J of gravitational potential energy while descending 4.73 m between floors. How much does the elevator weigh?
2.2kN
The relativistic energy of a 1000 kg car moving at 0.95 times the speed of light is:
2.9x1020 J
A bat moving at 90 km/h strikes an oncoming ball moving at 110 km/h. If the batter follows through so that the speed of the bat doesn't change during the hit and the coefficient of restitution of the ball is 0.6, what speed does the batted ball have after it has been struck?
210 km/h
An antique carousel that's powered by a large electric motor undergoes constant angular acceleration from rest to full rotational speed in 3.35 seconds. When the ride ends, a brake causes it to decelerate steadily from full rotational speed to rest in 11.1 seconds. Compare the torque that starts the carousel to the torque that stops it.
3.31
You operate a 120 W light bulb for 5 minutes. How much energy did you use?
36,000 J
A popular playground toy is a flexible seat that has automobile springs attached to it for a little bounce. When a 200 N child sits on the toy, it compresses 5 mm downward. What is the ride's spring constant?
40000 N/m
If you have a mass of 80 kg and are on a planet where the acceleration of gravity is 5 m/s2, your weight on the planet is
400N
Water weighs about 10 N per liter on Earth. A 4.0 liter ball is pushed underwater on the space shuttle, where gravity was 1/10 that on Earth. What is the buoyant force on the ball?
4N
To cause a 25 kg object to experience an acceleration of 2 m/s2 the net force that needs to be applied to the object is:
50N
The maximum height above the ground for a gymnast jumping straight upward with an initial speed of 10 m/s is about
5m
What is the gravitational force that two 100 kg persons exert on each other when standing 1m apart?
6.672x10-7 N
At a speed of 12 m/sec how far can you travel in one minute?
720m
How far apart would two 100 kg persons need to be so that the force they exert on each other is equal to 1N? You can assume they are point masses, having mass but no size.
8.17x10-4 m
The diameter of a pipe is tripled while the pressure difference across the pipe remains the same. The volume flow rate of the pipe increases by a factor of
81
The coefficient of restitution for a particular ball is 0.7. If the ball rebounds from surface traveling at 60 m/s its collision speed was
85.7 m/s
The relativistic momentum of a 1000 kg car moving at 0.95 times the speed of light is:
9.13x1011 kg m/s
When you push down on the handle of a doll-like wooden nutcracker, its jaw pivots upward and cracks a nut. If the point at which you push down on the handle is 5.05 times as far from the pivot as the point at which the jaw pushes on the nut, how much force will the jaw exert on the nut if you exert a force of 18.7 N on the handle? (Assume that all forces are at right angles to the lever arms involved.)
94.435N
Suppose you weigh 986 N. How much force does the Earth exert on you, if any?
986N
Which system is in a state of stable equilibrium?
A marble in the bottom of a spherical bowl.
You are watching a science fiction movie where people on a space ship are traveling around the universe observing stars with different temperatures. Which of the following stars has the lowest surface temperature?
A reddish star
Which of the following would cause a household fan to stall?
A. The blades are too sharply angled for the speed the fan rotates. B. The fan is rotating too fast. *Both A and B*
Suppose you are riding on a merry - go - round and you move out to the edge. Why does the rotational rate of the system decrease?
Angular momentum is conserved and the moment of inertia increased.
When a baseball player hits a ball, the bat can respond by
Any combination of these choices.
Why will a rolled - up ball of aluminum foil float in water but solid aluminum will sink?
Due to the air inside, the average density of the ball is lower than water.
Why are good thermal conductors generally good electric conductors also?
Electron motion is responsible for determining both properties.
Which of the following quantities is not conserved?
Entropy
Which Law of Thermodynamics relates change in internal energy to heat added to a system and work done by it?
First
Force and momentum are related in that:
Force is a change in momentum per unit time
An object pivoting about its center of mass is
Free of net torque
Why does the handle of a metal spoon submerged in boiling soup feel hot ?
Heat from the soup is transferred through the spoon by conduction.
Why does an ice cube feel cold?
Heat from your hand enters the cube by conduction.
When a fluid is in steady - state flow and its path bends, the pressure on the outside of the bend is always
Higher than the pressure on the inside of the bend.
Your apparent weight is equal to your weight
In an elevator not accelerating.
At what place in or near the jet engine is gas moving the fastest relative to the flying airplane?
In the plume of exhaust gas flowing out of the engine's outlet duct.
A child is riding a bike and skids to a stop. What happens to their kinetic energy?
It is turned into heat by sliding friction.
Suppose the moon's angular velocity is halved. By what factor will its rotational kinetic energy change?
It will decrease to ¼ its original value.
A mechanic balances the wheels of your car to make sure that their centers of mass are located exactly at their geometrical centers. Neglecting friction and air resistance, how would an improperly balanced wheel behave if it were rotating all by itself?
It would wobble because gravity would produce a net torque on it.
The surface of the moon is exposed to full solar radiation because it has no atmosphere. Why then does the moon not heat up endlessly until it disintegrates?
Its temperature rises until it is able to radiate heat away into space as fast as it arrives from the sun.
Which temperature scale has 373 as the boiling point of water?
Kelvin
When a fish hovers over the bottom of a lake, what forces act on it, and what is the net force?
Lift and weight, for a net force zero.
Suppose you are driving your car down the highway and speeding up. Which of the following are true?
Neither the car's kinetic energy nor momentum are constant.
Suppose you go from the Earth to a planet where the acceleration of gravity is 3 m/s2. On the new planet your mass will:
Not change
It is possible for two objects of equal mass to have different rotational masses because
Rotational mass depends on total mass and mass distribution.
Suppose you are driving north and suddenly hit your brakes to avoid a dog in the road. As you come to a stop your acceleration is directed:
South
Suppose you are riding a bicycle. If you want to waste as little energy as possible while the bike is in motion, what type of friction should exist between the bike and the road?
Static
What type of friction causes bearings to not waste much energy?
Static
As you twist the ball, you find that its rate of rotation increases very slowly, even though you are twisting it as hard as you can. Why does the ball's angular velocity change so slowly?
The ball has an enormous rotational mass.
You fill two identical mugs with coffee, but the coffee in one mug is at a higher temperature than that in the other mug. You place the two mugs simultaneously in a microwave oven and turn it on briefly. As a result, you add 1 joule of thermal energy to each mug. Which mug experiences the larger increase in entropy (if any)?
The mug containing the colder coffee experiences the larger increase in entropy.
Power is
The rate at which energy is used, stored, created, dissipated, etc.
Some racing cars are designed so that their massive engines are near their geometrical centers. Why does this design make it easier for these cars to turn quickly?
The rotational mass is smaller with this design, so a larger angular acceleration (quicker turn) is possible.
Why do balls that deform bounce poorly?
They dissipate energy in an unrecoverable form.
Why do elastic balls bounce so well?
They store energy through compression, like a spring.
Suppose you are spending your weekend on roller skates trying to get momentum from somewhere. Which of the following will give you momentum in the north direction?
Throwing your keys southward.
When the ball was made, the sculptor carefully adjusted its center of gravity to lie exactly at its geometrical center. Why?
To ensure that the ball is balanced and therefore free of gravitational torques.
Why are failures in dams more likely to occur closer to the bottom of the dam?
Water pressure is higher at the bottom.
Under what conditions are the values of average speed and the magnitude of the average velocity equal?
When moving in a straight line and not turning around
A bathroom scale reads:
Your apparent weight
The air in this room consists of countless tiny, independent molecules. You can be sure that all the oxygen molecules will not all shift spontaneously to the other side of the room (leaving you without oxygen) because that would
be extremely unlikely and therefore violate the 2nd law of thermodynamics.
When moving, a bicycle is in a state of dynamic equilibrium due to which of the following?
both gyroscopic effects and the shape of the fork
A curve ball's path bends to the right as it flies toward home plate because it is experiencing an aerodynamic force to its right. One reason why the ball is experiencing this aerodynamic force is that the ball is spinning and that spin
causes the air to flow more rapidly around the right side of the ball than around the left side of the ball.
The _______ two temperatures are the _______ it is to move heat from hot to cold.
closer; easier
The first law of thermodynamics is a re - statement of the law of _________________.
conservation of energy
The gulf stream is one of nature's ways of transferring energy through
convection
Wind is one of nature's ways of transferring energy through
convection
Ice is ___________.
crystalline
Aerodynamic forces consist of
drag and lift.
In order to do a positive amount of work you must:
exert a force and move in the direction of the force
As the Reynolds number decreases,
flow is going from being viscous dominated to inertia dominated and therefore turbulent.
The maximum speed a rocket can achieve is
greater than the speed of its exhaust plume but less than the speed of light.
Suppose you have two containers with liquid in them. One has a density of 760 kg/m3 and the other has a density of 910 kg /m3. If an object floats in one container and sinks in the other, the density of the object
has a value between 760 kg/m3 and 910 kg/m3.
In a car engine, the compression stroke involves the piston compressing the air/gas mixture so rapidly that virtually no heat loss can occur. In the compression stroke, the air/gas mixture
heats because work is being done on the air/gas mixture.
Flowing honey is less likely to become turbulent than flowing water because
honey's large viscosity favors laminar flow.
The "strokes", or "cycles" in a four - stroke engine are ____________________.
induction, compression, power, exhaust
A Diesel engine is more efficient than a gasoline engine because
it has a higher temperature and can therefore convert more heat into work.
A shiny, white transparent surface prevents heat transfer because
it has emissivity of zero and reflects all light that strikes it.
An object is in stable equilibrium only when
its total potential energy rises whenever it reorients.
Compared to planets close to the sun, and based upon Kepler's third law of planetary motion, the length of the year of planets farther out from the sun are
larger
A curve ball in baseball curves because of
lift forces
The SI units of acceleration are:
m/s^2
A fan can be used to circulate air around a room. The pressure at the inlet side of the fan is
more than the pressure at the outlet side.
If a golf ball were smooth rather than dimpled, it would
not travel as far after being hit by a golf club.
If you need to harness energy in order to do a particular job, the type of energy needed is
ordered energy
Melting is a _____________ that requires energy ________ for the melting system.
phase transition; input
Freezing is a ____________ that requires energy ________ for the melting system.
phase transition; release
Gravity creates
pressure gradients in fluids.
Rockets receive their forward propulsion through
pushing against the exhaust.
Suppose your car's speed doubles. By what factor will its kinetic energy change?
quadruple
Low-E coatings are placed on house windows because
radiative heat transfer is a big problem for clear windows but the Low - E coating reflects infrared light.
"The entropy of an isolated system never decreases." Which Law of Thermodynamics is this?
second
A three - wheeler is
statically stable and dynamically unstable.
A motorcycle is
statically unstable and dynamically stable.
Suppose that you place a timer and a tiny pile of gunpowder in an absolutely rigid box. You then seal the box completely and insulate it perfectly so that no heat can flow in or out of the box. Soon the timer ignites the gunpowder and it burns to form smoke. Since the box is sealed, the smoke remains inside it. If you look into the box a few minutes later, you will find that the smoke has not converted back into the gunpowder because
such an event, unburning the smoke to form gunpowder, is extraordinarily unlikely.
Moments before it is ignited by the spark plug, the mixture of fuel and air inside an automobile cylinder is compressed to very high density. During the compression process, the mixture's
temperature rises dramatically and so does its pressure.
Fluids have viscosity because
the atoms and molecules within the fluid interact with each other, producing internal frictional forces.
You are riding in a hot air balloon. You have not used the burner for some time and the balloon begins to sink. Assuming that no air is allowed to leave or enter the balloon,
the average density of the balloon became greater than the surrounding air and the buoyant force on the balloon became less than its weight.
In studying many martial arts, it is necessary to practice efficient and safe postures. One important concept related to how one should stand is that the feet should be reasonably far apart, because
the base of support is wider, thus stabilizing the person.
A thermoelectric cooler is a type of heat pump that uses electric power to move heat against its natural direction of flow. In other words, it takes energy from a system and transfers it to another system which is at a higher temperature. In such a heat pump
the cooler requires power input because the flow of heat from a cool region to a warm region alone would decrease the entropy (disorder) of the system.
Housing and natural animal insulation works because
the insulating materials trap air and prevent convection.
When cooking a potato in a conventional oven it is useful to stick a nail in it, which makes it cook faster. This is because
the nail is a good conductor of heat.
When driving down a level smooth road, your car tires flatten at the bottom and they nicely support the weight of your car. However when you run over a small pointed rock the tire is punctured and fails. The rock is able to puncture the tire because
the small surface area of the rock times the pressure in the tire is not enough force to support the car. Thus, the tire fails.
You are watching a semi truck bounce up and down on a spring. (Yep it's a toy!) At the topmost point in the truck's path,
the truck's velocity is zero but its acceleration is downward.
For an object that sinks in a fluid,
the weight of fluid displaced is less than its weight.
For an object that is floating on a fluid,
the weight of the fluid displaced equals the object's weight.
For an object that is neutrally buoyant in a fluid,
the weight of the fluid displaced equals the object's weight.
Astronauts in the space shuttle feel weightless because
they are in a constant state of free - fall.
During a football game the ball is kicked and it travels across the field. If the ball is kicked away from its center of mass it will
translate and rotate
You open the refrigerator in your room and put in a case of room-temperature root beer. After an hour, the root beer is ice cold. If your room air did not exchange any heat with the outdoor air during that time, the room air will be
warmer because the refrigerator will have pumped heat out of the root beer and into the room air.
The four things that affect the amount of water flowing through a hose are
water viscosity, hose length, inlet and outlet pressures and hose diameter.
In a popular classroom demonstration, a cotton ball is placed in the bottom of a strong test tube. A plunger fits inside the tube and it makes an air - tight seal. It is then pushed down very rapidly, and the cotton flashes and burns. This happens because
when the air was compressed its temperature increased.