Homework Review Physics
If an object suspended by a scale shows a weight of 3 N in air and 2 N when submerged in water, the buoyant force on the submerged object is __________.
- 1 N
What is the acceleration of a car moving along a straight road that increases its speed from 0 to 100 km/h in 10 s?
- 10 km/h·s
A force of 50 N is applied to the end of a lever, which is moved a certain distance. If the other end of the lever moves one-third as far, how much force does it exert?
- 150%
If the skater started from rest 4 mm above the ground (instead of 7 mm), what would be the kinetic energy at the bottom of the ramp (which is still 1 mm above the ground)?
- 2205J
In a simple machine, how much work is done when an input of 10 N acts over a distance of 5 m?
- 50 J
If an input of 100 J in a pulley system increases the potential energy of a load by 60 J, what is the efficiency of the system?
- 60%
When the useful energy output of a simple machine is 100 J, and the total energy input is 200 J, the efficiency is _______.
50
Why did the particles jiggle around?
The particles were struck by atoms, but unequally on different sides.
Why is a blob of bread dough said to be inelastic?
When deformed, it does not return to its original shape
Which varies with location, mass or weight?
weight
Why doesn't the Leaning Tower of Pisa topple over?
- A vertical line through the center of gravity passes inside its support base.
Why does the bowling ball behave the way it does the first time Dr. Hewitt lifts the bowling ball near his teeth and lets go?
- All of the initial energy of the ball was converted completely back to potential energy when the ball returned.
Why is physics considered to be the basic science?
- Because all other sciences can be shown to be derived from it.
Why does bending your legs when running enable you to swing your legs to and fro more rapidly?
- Bending your legs shortens them, thus reducing rotational inertia.
How does water pressure 2 mm below the surface of a small pond compare with water pressure 2 mm below the surface of a huge lake?
- Both pressures would be the same
Which of the following are negatively charged?
- Electrons
Is it momentum or energy that enables an object to do work?
- Energy
To increase the momentum of an object, should you exert a large force, or extend that force for as long a time as possible--or both? Explain.
- Exert a large force over the longest time because momentum is proportional to both force and time.
What is required to change the angular momentum of a system?
- External torque
What did Galileo discover in his legendary experiment on the Leaning Tower of Pisa?
- Galileo found that a heavier stone does not fall significantly faster than a lighter one.
The experimenter from the video rotates on his stool, this time holding his empty hands in his lap. You stand on a desk above him and drop a long, heavy bean bag straight down so that it lands across his lap, in his hands. What happens?
- He spins slower.
What is the most abundant element in the known universe?
- Hydrogen
If it falls, what becomes of this energy just before it hits the ground? When it hits the ground?
- Immediately before hitting the ground the peach's energy is kinetic energy; when it hits the ground, its energy becomes thermal energy.
Is inertia the reason for moving objects maintaining motion, or is it the name given to this property?
- Inertia is the name for the property of matter.
Fill in the blanks: Newton's first law is often called the law of ____; Newton's second law is the law of ____; and Newton's third law is the law of ____.
- Inertia, acceleration, action -reaction
What type of path does a moving object follow in the absence of a force?
- It continues to move in a straight line at a constant speed.
How does the force needed to turn the wrench change if you increase the lever arm?
- It decreases.
How does the lever arm change if you decrease the angle of the force?
- It decreases.
How does the lever arm change when you decrease the distance to the nut?
- It decreases.
How does one isotope differ from another?
- It has a different number of neutrons
Compared with some original speed, how much work must the brakes supply to stop a car that is moving twice as fast? How will the stopping distance compare?
- It takes four times the work and four times the stopping distance.
If it were raised twice as high, how much more potential energy would it have?
- It would have twice as much potential energy.
Calculate the kinetic energy of a 108-kgkg scooter moving at 12 m/sm/s
- KE = 7800 J Kinetic energy = 1212 mass ×× speed 22 : KE = 12mv2
Distinguish between mass number and atomic mass.
- Mass number is the number of nucleons; atomic mass is the total mass of an atom.
Are most of the atoms around us younger or older than the Sun?
- Most are older than the Sun
How many forces act on an object in free fall?
- One force, the force due to gravity.
Select the correct equations that show that 50 WW of power is required to impart 100 JJ of energy to something in 2 ss.
- P=W/t=(100J)/(2s)=50W
Dan and Sue cycle at the same speed. The tires on Dan's bike are larger in diameter than those on Sue's bike. Which wheels, if either, have the greater rotational speed?
- Sue's wheels have the greater rotational speed.
If the mass of a sliding block is doubled while a constant net force is applied, by how much does the acceleration change?
- The acceleration is reduced to half of its original value.
If the mass of a sliding block is somehow doubled at the same time the net force on it is doubled, how does the resulting acceleration compare with the original acceleration?
- The acceleration remains the same.
What happens the second time Dr. Hewitt lifts the bowling ball near his teeth and gives it a push?
- The ball leaves Dr. Hewitt and returns to him, going past the point where it was released.
What happens the first time Dr. Hewitt lifts the bowling ball near his teeth and lets go?
- The ball returns to Dr. Hewitt, stopping almost exactly at the point where it was released
What is the buoyant force that acts on a submerged object equal to?
- The buoyant force is equal to the weight of the fluid displaced by the submerged object.
If you place a Styrofoam cup on the table and a bunch of BBs move around it randomly, what will happen to the cup, and why?
- The cup will move randomly in different directions because the BBs will exert unequal forces on the cup in different directions.
Suppose you increase the depth of the object WITHOUT changing its height. What will happen to the force due to pressure on the bottom of the object?
- The force due to pressure on the bottom of the object will increase.
Suppose you increase the height of the object WITHOUT changing its depth under water. What will happen to the force due to pressure on the bottom of the object?
- The force due to pressure on the bottom of the object will increase.
How long does that force last after the ball leaves your hand?
- The force you exert on the ball ceases as soon as contact with your hand ceases.
If you push on a crate with a horizontal force of 120 NN and it slides at constant velocity, how much is the friction acting on the crate?
- The frictional force on the crate is 120 NN opposite the direction of motion.
How does the minimum force needed to hoist a load change as you increase the number of pulleys from one to two, then three, then four?
- The minimum force needed to hoist the load becomes half, then one-third, then one-fourth.
Suppose you increase the height of the object WITHOUT changing its depth under water. What will happen to the net buoyant force?
- The net buoyant force will increase.
Suppose you increase the depth of the object WITHOUT changing its height. What will happen to the net buoyant force?
- The net buoyant force will stay the same.
What is the net force on a cart that is pulled to the right with 100 pounds of force and to the left with 30 pounds of force?
- The net force is 70 pounds to the right
What is the net force on an object that is pulled with 80 NN to the right and 80 NN to the left?
- The net force is zero newtons.
Why does the buoyant force act upward on an object submerged in water?
- The pressure upward on the deeper bottom is greater than the downward pressure on the top.
Which has a greater momentum, a heavy truck at rest or a mouse running along the street?
- The running mouse
What is the speed acquired by an object in free fall 4 ss after being dropped from a rest position?
- The speed is 40 m/sm/s.
How does the travel distance of the load change as you increase the number of pulleys from one to two, then three, then four?
- The travel distance of the load becomes half, then one-third, then one-fourth.
Predict what will happen if you reduce the magnitude of the velocity of the green truck to a magnitude smaller than that of the red truck.
- The trucks will stick together after the collision and move to the left.
Now, predict what will happen if you change the velocity of the red truck so that it has a magnitude smaller than that of the green truck but is negative.
- The trucks will stick together after the collision and move to the right.
Now, predict what will happen if you change the velocity of the red truck so that it has a magnitude smaller than that of the green truck but is positive.
- The trucks will stick together after the collision and move to the right.
Now, predict what will happen if you increase the mass of the green truck so that it is greater than the mass of the red truck.
- The trucks will stick together after the collision and move to the right.
predict what will happen if the red and green truck with equal mass and equal magnitude of velocity collide.
- The trucks will stick together after the collision and not move.
When you push against a wall, what pushes back?
- The wall pushes back
When Dr. Hewitt pulls the tablecloth, why do the items on the tablecloth do what they do?
- Their inertia is sufficient to keep them there.
Calculate the torque produced by a 60-NN force when a pipe extends the length of the wrench to 0.50 mm
- Torque = Lever Arm ×× Force30 N⋅m
According to Hooke's law, if you double the force when stretching a spring, the elongation of the spring is normally __________.
- Twice as much
Whenever a net force acts on an object, there is a change in the object's _______.
- Velocity
What is the main difference between speed and velocity?
- Velocity includes a direction, but speed does not.
With respect to volume, mass, and density, which changes when you squeeze a loaf of bread? What doesn't change?
- Volume decreases, mass stays the same, density increases
What do we call the quantity force multiplied by distance?
- Work
A bowling ball at rest is in equilibrium. Is the ball in equilibrium when it moves at constant speed in a straight-line path?
- Yes, the bowling ball is in equilibrium because ΣF=0ΣF=0.
Earth pulls down on you with a gravitational force that you call your weight. Do you pull up on Earth with the same amount of force?
- Yes, you pull up on Earth with the same force.
Newton said that something was needed to change the motion of an object. A clear reading of his first law tells us that what is needed is ______.
- a non-zero net force
As the skater is skating back and forth, where does the skater have the most potential energy?
- at its maximum value at the locations where the skater turns and goes back in the opposite direction.
Where on the track is the skater's kinetic energy the greatest?
- at its maximum value at the lowest point of the track.
When traveling twice as fast your kinetic energy is increased _______.
- by four times
The pressure increases on a block resting on a table when you increase the __________.
- downward force on the block
The kinetic energy at the bottom of the ramp is
- equal to the amount of potential energy loss in going from the initial location to the bottom.
The buoyant force on a floating object is __________.
- equal to the object's weight
Why does the bowling ball behave as it does when Dr. Hewitt lifts it and gives it a push?
- he extra energy from the push is converted into kinetic energy, which is then converted into more potential energy at the end of the motion than the ball had when it was released.
n what factors does the buoyant force acting on an object depend?
- height of the object
When the skater starts 7 mm above the ground, how does the speed of the skater at the bottom of the track compare to the speed of the skater at the bottom when the skater starts 4 mm above the ground?
- higher, but less than twice as fast.
Rotational inertia of an object rotating about an axis becomes greater with _______.
- increased mass and increased distance to mass concentration
Surface tension is caused by __________.
- molecular attractions
The direction of the force of friction on a sliding crate is _______.
- opposite to the direction of sliding
With the "Pulleys" slider set at 1, predict the minimum force needed to hoist the load. You may want to pay attention to the provided force diagram -- in particular the size of the upward force compared to the downward force.
- slightly greater than 250 N
What did Robert Brown see under the microscope?
- specks of dust moving around
The force that propels a rocket is that provided by _______.
- the expelled gas pushing on the rocket
Observe the total energy bar on the Bar Graph. As the skater is skating back and forth, which statement best describes the total energy?
- the same at all locations of the track.
When a cue ball strikes an 8 ball head-on in a game of pool, the cue ball _______.
- transfers its momentum to the 8 ball
A crate sits at rest on a factory floor. Friction between the crate and floor occurs _______.
- when the crate is pushed horizontally, whether sliding or not
When two vehicles collide, momentum is conserved _______.
- whether the collision is elastic or inelastic
How does the volume of a completely submerged object compare with the volume of water displaced?
-The volumes are equal.
What is the net force on the book?
0 newtons
What is the net force when a pair of 5-N forces simultaneously act in the same direction on an object?
10 N
What is the weight in newtons of a 1-kilogram brick resting on a table?
10 N
Consider again the case where the skater starts 7 mm above the ground and skates down the track. What is the skater's speed when the skater is at the bottom of the track?
11 m/sm/s - For a 75-kgkg object having approximately 4410 JJ of energy, the speed must be roughly 11 m/sm/
A 12-NN book is at rest on a flat table. How many newtons of support force does the table provide?
12 newtons up
Which requires more work--lifting a 50-kgkg sack vertically 2 mm or lifting a 25-kgkg sack vertically 4 mm?
Both take the same 1000 J
When Dr. Hewitt pulls the tablecloth, what happens to the items on the tablecloth?
They tend to stay where they were.
