Physics 101 Review
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?
0.4 m
A ball hits a wall going 10 m/s, and bounces off going 7 m/s. The coefficient of restitution is
0.70
Bolts work because they act like very strong springs and extend slightly when they are tightened. Suppose a steel bolt has spring constant 1.8x108 N/m. How far would it have to stretch in order to provide a force 2000N?
1.11x10-5 m
Atmospheric pressure is about 100000 Pa. At what depth in water does this pressure double?
10 m
The car is moving at 10 m/s relative to Bill (Bill is moving 5m/s). How fast does Amy see the car as moving?
15 m/s
If you double the absolute temperature of a star, its power output increases by a factor of
16
You push on a box with a horizontal force of 20 N and the box moves a distance of 8 m. The amount of work you have done on the box is
160 J
You work in a clock shop and are dealing with an irate customer whose clock you are restoring. They notice that the period of the pendulum in their clock is 2 s and they want to double it. So they insist that you replace the pendulum with one of the same dimensions but just heavier. So you do this. When you get the clock repaired, you and the customer check out the clock's period and find it to be
2 seconds
Suppose you do 1000 J of work on a 5 kg object, and all the work went into lifting it above the ground. How high above the ground will the object be when all the work has been done?
20 m
The onset of turbulent flow happens for a Reynolds number of about
2300
During one cycle, an automobile engine takes in 12,000 J of heat and discards 9000 J of heat. What is the efficiency of this engine?
25%
A machine uses 1000 J of electric energy to raise a heavy mass, increasing its potential energy by 300 J. What is the efficiency of this process?
30%
An ideally efficient heater adds 1100 J of heat to a warm room. How much work does it perform if it removes 1400 J of energy from the outdoors?
300 J
The following pairs of temperatures represent the temperatures of hot and cold reservoirs for heat engines. Which heat engine has the highest possible efficiency?
300°C, 30°C - biggest degree separation
You operate a 120 W light bulb for 5 minutes. How much energy did you use?
36,000 J
You are swinging a tin can around your head in a perfectly horizontal circle of radius 4 m. (This is really not possible but we're saying it almost happens.) If the speed of the can is 4 m/s what is its acceleration?
4 m/s2
The brake system in most cars makes use of a hydraulic system. This system consists of a fluid filled tube connected at each end to a piston. Assume that the piston attached to the brake pedal has a cross sectional area of one half a square inch and the piston attached to the brake pad has a cross section area of two square inches. When you apply a force of 10 pounds to the piston attached to the brake pedal, the force at the brake pad will be,
40 pounds
If you have a mass of 80 kg and are in a planet where the acceleration of gravity is 5 m/s2, your weight on the planet is
400 N
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
The coefficient of restitution for a particular ball is 0.45. If he ball hits a surface traveling at 100 m/s its rebound speed will be
45 m/s
The maximum height above the ground for a the gymnast jumping straight upward with an initial speed of 10 m/s is
5 m
You walk in a given direction for 20 m during the first 5 seconds of a trip and then 15 m during the next 2 seconds. Your average speed is equal to
5 m/s
A car starts from rest and accelerates at 4 m/s2. How much time will it take the car to reach a speed of 20 m/s?
5 s
What is the frequency of a vibration with period 0.02 second?
50 Hertz
In Europe an electric razor completes 50 vibrations in 1 second. The frequency of these vibrations is
50 Hz with a period of 1/50 second
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
50 N
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?
720 M
You are swinging a tin can around your head in a perfectly horizontal circle of radius 4 m. (This is really not possible but we're saying it almost happens.) If the speed of the can is 4 m/s and its mass is 2 kg, what inward force is required to keep the can moving in the circle?
8 N
You are bored during the summertime when school is not in session and you decide to do an experiment where you compare the properties of water and air. If the density of air is 1.25 kg/m3 and the density of water is 1000 kg/m3 , what volume of air weighs the same as 1 liter of water?
800 liters
The fundamental frequency of a violin string is 440 hertz. The frequency of its second harmonic is
880 Hz
Suppose you weigh 986 N. How much force does the Earth exert on you, if any?
986 N
Water weighs about 10 N per liter. A 4.0 kg ball floats on the water's surface. What is the weight of the water being displaced by the ball?
About 40 N
What two properties of a material affect the speed of sound in the material?
Density and phase
Force and momentum are related in that:
Force is a change in momentum per unit time
Consider the Moon orbiting the Earth. _______ is the centripetal force for the orbit, and one could therefore measure the mass of the ________ by studying the Moon's orbit.
Gravity:Earth
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
A Diesel engine is more efficient that a gasoline engine because
It has a higher temperature and can therefore convert more heat into work
Suppose you have a car traveling down the road at constant speed and not changing direction. It is experiencing gravity, wind resistance and frictional forces from the road. What can be said about the car's acceleration?
It is not accelerating because it has constant velocity.
An object is in stable equilibrium only when
Its total potential energy rises whenever it reorients.
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.
You are swinging a 2 kg tin can around your head in a perfectly horizontal circle of radius 1 m with a speed of 6 m/s. (This is really not possible but we're saying it almost happens.) If the string can safely exert a force of 30 N will it be able to swing the can?
No because the required force is 36 N.
In the constellation Orion, you can easily observe the difference between the reddish looking star Betelgeuse and the bluish looking star Rigel. Which of the two has the hotter surface temperature?
Rigel
It is possible for two objects of equal mass to have rotational masses because
Rotational mass depends on total mass and mass distribution in radial distance.
On a humid summer day, perspiration does not cool you off much. Why?
The air is almost saturated with water vapor and there is almost no net evaporation.
Suppose you have two cars, and the larger one is twice as massive as the smaller one. If you and a friend push on them so that their accelerations are equal, how must the forces applied to the cars compare?
The force on the larger car is twice that on the smaller car
In making ice cream, the flavored cream is in a container in contact with ice. In order to freeze the ice cream why is it essential to make the ice melt at a very low temperature?
The low temperature of the ice as well as its melting removes energy from the flavored cream, causing it to freeze.
Power is
The rate at which energy is used, stored, created, dissipated, etc.
You are hired as an engineer at a thermometer factory. Suppose you built a water thermometer by replacing the mercury in a mercury thermometer with water. You want to measure temperatures above freezing with it. How would it behave as the temperature drops from 5o C to 1oC?
The reading will decrease and then begin increasing.
Suppose that we are able to send astronauts to Mars and they engage in a game of golf on the red planet's surface. Given that the atmosphere on Mars is considerably less dense than our own, how will the path of the ball be affected?
There is less drag and gravity, so the ball will go further than if there were air.
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.
Cities have to use water towers to supply water to because
Water pressure at the bottom of the tower is much higher than at the top
Your dryer is broken, so you have to hang your wet clothes from the washing machine outside to dry. Under which conditions would your clothes dry fastest?
When it is 75°F with 50% relative humidity.
Which system is in a state of stable equilibrium?
a marble in the bottom of a spherical bowl
Suppose you are standing on a bathroom scale when you are flying in a jet airplane. For a moment the scale reads more than your actual weight. During that moment, it's exerting an upward force on you that is greater than your weight and you are
accelerating upward
The vibrations along a longitudinal wave move in a direction
along the wave
The loudness of a sound is most related to its
amplitude (intensity)
A baseball player balances a bat on his finger; the bat is laying sideways and not standing on end. The bat will balance
at its center of mass
Your apartment window opens 20 meters (65 feet) above a lemonade stand. Your friend lowers a long plastic tube out the window until its end enters the tank of delicious lemonade far below. She then begins to suck on the other end of the tube in hopes of getting a free drink. To her dismay, she never tastes a drop because
atmospheric pressure cannot support a column of lemonade 20 meters tall.
Suppose you go from the earth to a planet where the acceleration of gravity is 2.5 m/s2. On the new planet your weight will be about
be ¼ its value on Earth
When a sample of 0ºC water is heated, it first
contracts then expands
You are playing with your younger cousins and find yourself on all fours, with your hands and feet on four bathroom scales on the level ground. You took a "Physics in Everyday Life" course so you can make a reasonable guess that the reading on each scale is obtained by
dividing your mass by 4
If the mass of one planet is somehow doubled, the force of gravity between it and a neighboring planet would
doubles
The entropy of an isolated system
either increases or remains constant
which of the following qualities is not conserved?
entropy
In order to do a negative amount of work you must
exert a force and move opposite to the direction of the force.
For momentum to be conserved in a system it must
experience no net external force
If you are backing up but slowing down, your acceleration is directed
forwards
Suppose you are standing on a bathroom scale when you are flying in a jet airplane. For a moment the scale reads less than your actual weight. During that moment, it's exerting an upward force on you that is
greater than your weight
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
You are taking a shower in your dormitory when someone flushes a toilet nearby. The pressure in the cold water line drops and you find yourself showering in what feels like molten lava. This loss of cold water pressure occurs when the toilet lets cold water flow through the pipes delivering it to the bathroom and the water's speed in those pipes increases. Assuming all the piping to be about on the same level, the cold water's faster motion in the delivery pipes reduces its pressure in the shower head because faster moving water
has less pressure than slower moving water
The curves on bicycle racetracks are steeply banked, so that the inner edge of each curve is much lower than its outer edge. This banking tips the support force that the track exerts on the bicycle wheel toward the center of each turn. That center-directed or centripetal force on the bicycle is important because it
helps the bicycle accelerate inward to complete each turn without skidding.
The neighborhood children are playing and one has lost a pocketful of change. As a result they all decide to do a close inspection of the sidewalk. They notice that there are gaps in between the sidewalk filled with a felt - like material. These gaps will prevent
high stress due to thermal expansion
When you pour honey into a bowl, it flows smoothly. If you did the same with water, it would splash. These different behaviors occur because honey's
high viscosity keeps it flowing smoothly while water's low viscosity allows inertia to break its flow into many separate pieces.
Your apparent weight is equal to your weight
in an elevator not accelerating
A steady force pushes in the piston of a well-insulated cylinder. In this process, the temperature of the gas
increases
The "strokes", or "cycles" in a four - stroke engine are
induction, compression, power, exhaust
Noise-canceling devices such as jackhammer earphones make use of sound
interference
A child is riding a bike and skids to a stop. What happens to their kinetic energy?
it is dissipated by static friction
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
What does the period of a pendulum depend on?
length and gravity
A curve ball in baseball curves because of
lift forces
Two liquids, A and B, have equal masses and equal initial temperatures. Each is heated for the same length of time over identical burners. Afterward, liquid A is hotter than liquid B. Which has the larger specific heat?
liquid B
Low-pitched sounds have
low frequencies and long periods
When a 134-Hz tuning fork and a 144-Hz tuning fork are struck, the beat frequency is
more than 8 Hz
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
In a soccer game, someone has kicked the ball so that it is heading right toward your face. You want to slow the ball down with your arm. To execute your plan most effectively you should
move your arm in the direction that the ball is moving
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
A pedestrian bridge crosses a street. This bridge is entirely supported by columns from below. A gap at each end of the bridge separates the bridge's surface from the sidewalks leading to the bridge. The width of each gap changes with time. This width is smallest
on hot days
The vibrations along a transverse wave move in a direction
perpendicular to the wave
Melting is a ______ that requires energy ________ for the melting system.
phase transition; input
Suppose your car's speed doubles. By what factor will its kinetic energy change?
quadruple
Which type of heat transfer can happen efficiently through empty space?
radiation
Dimples on a golf ball hit without spin
reduce drag
If the mass of one planet is somehow doubled, the force of gravity between it and a neighboring planet would
reduces by one quarter
When an object is set vibrating by a wave having a frequency that matches the natural frequency of the object, what occurs is
resonance
A "bouncy" or "lively" ball bounces higher from a rigid, immovable surface than a "dead" ball does because the "bouncy" ball
returns more collision energy as rebound energy
When stringing telephone lines between poles in the summer, it is advisable to allow the lines to
sag
in which of these materials does sound travel fastest
steel
For the particular medium, the speed of sound varies with
temperature
Fluids have viscosity because
the atoms and molecules within the fluid interact with each other, producing internal frictional forces.
When you sit facing a campfire outdoors, your face feels quite warm because
the campfire is radiating heat towards your skin
The illustration shows a thermometer that uses a column of liquid (usually mercury or ethanol) to measure air temperature. In thermal equilibrium, this thermometer measures the temperature of
the column of liquid, the glass that encloses the liquid, and the air outside the thermometer.
When you drop a rubber ball on the floor and it bounces, the direction of its velocity reverses because
the floor exerts an upward support force on the ball and this force stops the ball's descent and eventually propels it upward.
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
The acceleration of an object is equal to
the rate of change of its velocity
Suppose you have an aquarium and you notice that you have a solid plastic decoration and a rock of about the same volume but twice as dense, and both are totally submerged in the water. The buoyant force on the plastic object is about ___________as that on the rock.
the same
You are watching a semi truck bounce up and down on a spring. At the topmost point in the truck's path
the truck's velocity is zero but its acceleration is downward.
Suppose you push horizontally on the wall of a building. For you to do work on the wall, which of the following need to happen?
the wall moves away from you
You are holding two identical-looking balloons, one filled with air and one filled with water. You drop these two balloons from a very tall bridge and notice that the water-filled balloon hits the ground first because it traveled faster. The object that experienced the larger amount of drag is
the water - filled balloon because it moved faster.
The spin cycle in your washing machine partially dries clothes by spinning them in a perforated metal basket. Such a process works because
the water leaves the basket moving tangent to the circular path
For an object that is floating on a fluid,
the weight of the fluid displaced equals the object's weight
You are riding an amusement park ride where you are strapped to the inside of a giant metal wheel that is rotating quite rapidly. Your acceleration is
toward the center
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.
A common glass thermometer contains a red or silver liquid that rises upward in a glass tube as the temperature of the thermometer increases. The liquid moves up the tube because
while both the glass and the liquid expand as their temperatures increase, the liquid expands more rapidly than the glass does.
A harmonic oscillator is an oscillator
with a restoring force proportional to its displacement from equilibrium
Your weight and mass are different in that
your weight depends upon local gravity but your mass does not.
