Download Second Semester Final Exam Preparation 2012

Second Semester Final Exam Preparation
Physics
Name:
Period:
Answer all of the following questions on your own paper. Leave plenty of room for each answer.
Conceptual Review:
CENTRIPETALFORCE AND UNIVERSAL GRAVITATION
1. What is centripetal force? What effect does a centripetal force have on an object?
2. You can make a simple device to detect acceleration (an accelerometer)
by hanging a fishing weight on a string under a protractor. While you
speed up, the fishing weight will hang at an angle behind its support so one
components of the string’s tension will pull it forward to make it
accelerate. While you slow down, the fishing weight will hang at an angle
in front of its support. What will happen when you drive in circles at a
constant speed? Why?
3. Everyone knows that there is no air on the Moon, but many people also imagine that there is no
gravity on the Moon. If you have ever watched video of the Apollo astronauts walking on the Moon, it
is clear that the Moon’s gravity holds the astronauts down. But even before we got to the Moon, we
were positive there would be gravity there.
a) What law of physics convinced us that the Moon had to have its own gravity? Why did we expect
the moon’s gravity to be weaker than the Earth’s gravity?
b) Could the Moon’s gravity affect us while we are still on the Earth? How would it affect you when
you are looking up at the moon above you in the sky? How would it affect you when it is on the other
side of the Earth?
MOMENTUM
4. During a game of disc golf, you are trying to throw your disc as far as possible when you throw your
first shot. To get the disc to go far, it needs to leave your hand traveling very fast. What can you do to
make the disc leave your hand going as fast as possible?
5. Nerf balls are intended to be safer to use than another ball with the same mass. What is it about Nerf
balls that make them less likely to hurt you or a piece of furniture or a pet or anything else that they run
into?
6. During a cartoon collision, Bugs Bunny stands still as he holds up his hand and stops a large artillery
shell from barreling into him. Why won’t this ever happen in the real world?
ENERGY
7. As a pickup truck glides at constant speed along flat ground, it does not do work on the sofa in the
truck’s bed. Explain how you can be sure that no work is done in this situation.
8. Explain how energy is conserved when you load an egg into a slingshot, pull it back, point the
slingshot straight up and release the egg. Detail what happens to the egg and what happens to the energy
during each stage of the egg’s journey.
9. When we studied orbits, we treated the Earth’s orbit
around the sun as a perfect circle. In reality the Earth’s
orbit is a slight ellipse, with the sun slightly off center (the
picture is exaggerated).
a) Based on the law of conservation of energy, how would
you expect the speed of earth in its orbit at aphelion to
compare to its speed at perihelion? Why?
b) It turns out that the summer half of the year (from the
vernal equinox to the autumnal equinox) lasts almost a
week longer than the winter half of the year (from the
autumnal equinox to the vernal equinox) in the northern
hemisphere [check a calendar if you don’t believe it]. Why
does our summer last longer than our winter? [Hint: what
part of our orbit are we in during the summer? During the
winter?]
FLUIDS AND PRESSURE
9. How do drinking straws work? Why do we say there is
no such thing as “sucking” in Physics?
10. Why do we use a knife to cut through butter and not the backside of a spoon?
11. Consider each situation. Decide whether the force of gravity, the buoyant force, and the pressure on
each block would be the same as or different than the other block for each of the following situations.
a) Two identical blocks of wood floating; one in water and one in mercury
b) Two balls of equal size held underwater; one ball has a greater mass than the other ball
c) Two balls of equal size and mass in a tub filled with oil: one held 10 m below the surface, the other
held 5 m below
12. What is Archimedes’s Principle?
13. How will the following affect the pressure of a fluid inside a container?
a) Increasing the volume of the container
b) Increasing the temperature inside the container
c) Increasing the number of molecules inside the container
14. Where does the buoyant force come from?
15. What is the pressure right at the surface of a body of water (where the depth is zero)? Where does
this pressure come from?
WAVES AND SOUND
16. What determines the period of a pendulum? What determines the period of a mass-and-spring
system?
17. What is the difference between a longitudinal and a transverse wave? Give an example of both.
18. What is it that “sets” the following wave properties?
a) Frequency
b) Velocity
c) Wavelength
19. How do the frequency and amplitude of a sound wave affect how we hear that sound?
20. Use the terms standing waves, natural frequencies, forced vibrations, and resonance to describe how
instruments work.
21. a) What are the two ways a wave can reflect? What determines how a wave will reflect?
b) What are the two ways that waves can interfere? How would the two types of interference between
two sound waves affect what we would hear?
22. What is the difference between the standing waves in an open-open tube and an open-closed tube?
How do these standing waves affect the natural frequencies of the tubes?
23. How does the air-filled tube of a bassoon turn the many frequencies of the reed’s buzzing into a nice
clean tone? What happens to make the desired tone sound loudly? What happens to all of the other
frequencies in the reed’s buzzing?
Calculation Practice:
1 A 70 kg water skier holds onto the 30 m long tow rope as the boat drives in a tight circle and the skier
swings in a circle at the end of the rope at a constant speed of 20 m/s. How much tension does the rope
exert on the skier?
2. NASA builds a gravitometer (a device for measuring the pull of gravity) to use in spaceships that will
land on other worlds. The gravitometer consists of a 0.00001 kg mass on the end of a fine spring that
will stretch when gravity pulls on the mass.
a) How much will the mass weigh if the spaceship lands on the surface of Mars?
b) The spaceship lands on an unknown moon, whose radius is 1500 km and the mass on gravitometer
weighs 6.5 x 10-5 N. How massive is the moon?
3. A 0.5 kg basketball is being dribbled. It is heading downward at 15 m/s when it hits the floor and has
a force of 220 N push it upward until it bounces off the floor at 12 m/s. How long is the ball in contact
with the floor?
4. One summer evening, sad because you haven’t learned any physics that day, you take a radar gun to
the carnival and watch the collisions of the bumper cars.
i) One collision you observe has a 160 kg bumper car heading east at 7.1 m/s run head on into a 180 kg
bumper car going 4.8 m/s to the west. After the collision, the first bumper car is heading west at 5.5
m/s.
a) How fast is the second car going?
b) How much energy do the two cars have before the collision? [Hint: what kind of energy does
each car have? How much?]
c) How much energy do the two cars have after the collision? [Hint: what kind of energy does each
car have? How much?]
d) Compare your answers to b) and c). Are they the same or different? Does this make sense?
Why or why not?
ii) In another collision, a 150 kg car headed south at 7 m/s runs down the car in front of it, which was
going 4 m/s also to the south. After the collision, both cars are still going south, the first car at 5 m/s and
the second car at 6.5 m/s.
a) How massive is the second car?
b) How much energy do the two cars have before the collision?
c) How much energy do the two cars have after the collision?
d) Compare your answers to b) and c). Are they the same or different? Does this make sense?
Why or why not?
5. You grab a piece of clothing on a clothesline and start walking away with it before it is completely
clear of the line. You pull with 30 N at 40 below horizontal while you walk 0.6 m horizontally before
realizing something is wrong.
a) How much work do you do on the clothesline?
b) How much energy does the clothesline have when you are done pulling? What kind of energy?
6. When you inherit some land, you decide to
build a frictionless roller coaster on it. The 300
kg rollercoaster car will start by dropping off a
high hill and then go through a 25 m diameter
circular loop, after which it will go over a 21 m
high hill (as shown in the picture)
a) How fast does the rollercoaster car have to
be going in order to stay on the track at point
B? (in other words, what is the slowest
possible speed for which it will make it
around the loop without coming off?)
b) How high do you need to build the hill at point A in order for the rollercoaster car to have enough
speed to stay on the track when it gets to point B?
c) How fast will the rollercoaster car be going when it gets point C if it barely makes it round the
loop at point B?
d) How much normal force does the track exert on the car at point C?
7. A 0.18 kg Hot Wheels car is placed into a spring loaded launcher and is pushed backwards10 cm
with 30 N of force. When the launcher is released, the car rushes out of the launcher and glides across
the floor for 10 m before coming to a stop. How strong is the force of friction against the car?
8. a) Calculate the force of the atmosphere acting on the top of a table that measures 1.6 m x 2.9 m.
b) What is the force of the atmosphere on the bottom of the table?
9. a) How much pressure does any one of the four legs holding up a 60kg loudspeaker exert on the
floor, if the legs are circular with a 2 cm diameter on the bottom?
b) How much pressure does a 1500 kg elephant standing on one foot (0.08 m2) exert on the floor?
10. a) An oak wood block with a volume of 1.3 x 10-4 m3 and a mass of 0.10 kg is halfway submerged
underwater (density of water = 1,000 kg/m3).
i. What is the force of buoyancy on the block?
ii. Will the oak block float, sink, or rise at this point?
iii. What is the pressure on the block when it is at the surface?
b) The oak block is then held fully submerged 3 m below the surface of the water.
i. What is the force of buoyancy on the block?
ii. Will the oak block float, sink, or rise at this point?
iii. What is the pressure on the block when it is 3 m below the surface?
11. a) Calculate the number of particles inside a helium-filled balloon that has a volume of 0.001 m3 if
the temperature inside the balloon is 22° C and the pressure inside is 130,000 Pa.
b) If the temperature is raised 5° C and the volume remains constant, what is the pressure inside the
balloon?
12. A tsunami wave with a frequency of 18 Hz travels at 120 m/s at it passes a warning buoy that is
anchored 500 m from the shoreline.
a) What is the wavelength of the wave?
b) How much time do people on the beach have to get out of the way of the tsunami?
13. Kelcie plays a flute, which works as an open-open tube. With all of the holes closed, it is 0.5 meters
long. She blows across the embouchure to create a hissing that includes all frequencies between 200 Hz
and 1100 Hz.
a) What frequency or frequencies will you hear loudly as Kelcie plays?
b) If she were to close off the far end of the flute with her hand while continuing to blow the same way,
what frequency or frequencies of sound would you hear loudly?
c) How does the pitch of the covered flute sound in comparison to the uncovered flute?
14. A 714 Hz sound wave resonates with the 5th harmonic in an open-closed tube of air. How long is
the tube?
15. a) How long does it take sound to travel 1 mile (about 1600 m)?
b) How long does it take light to travel that same distance? (Light travels at 300,000,000 m/s)
c) What is the time-delay between the moment you see lightning strike one mile away, and the moment
you hear the crack of thunder from that lightning strike?