The Physical World Midterm (chs 1-5)
A ball is allowed to drop from rest. If the upward direction is positive, then after 2 seconds its velocity will be
-19.6 m/s
The study of everyday phenomena allows us to
-Develop an understanding of the concepts used to describe more abstract concepts -Develop an appreciation of the physical universe around us -Develop out intuition and adjust our "common sense" to understand these phenomena
Physical Sciences
-Physics -Chemistry -Geology -Astronomy, etc.
An acceptable explanation must...
-agree with what is observed -predictions that can be tested -stand up to criticism
Theories
-created to explain observation -involves mathematics -will make predictions
Observation
-first step toward scientific theory -requires imagination
A student releases a ball from rest on an inclined plane and measures that it travels a distance of 0.8 m in a time of 4.0s. The average speed of the ball is
.2 m/s
You toss a ball straight up in the air. At the highest point, the ball's velocity is ______ and the acceleration is _____
0; downward
Steps in the scientific method
1. Careful observation of natural phenomena 2. Formulation of rules or empirical laws based on generalizations from these observations and experiments 3. Development of hypotheses to explain the observations and empirical laws and the refinement of hypotheses into theories 4. Testing of the hypotheses or theories by further experiment or observation
Assuming g = 10 m/s2 and that air resistance is negligible, in 1/2 second a ball dropped from rest will fall
1.25 m
A car starts from rest and after 10s is traveling at 30 m/s. Assuming that is continues to accelerate at the same rate it will take another ___ seconds to reach 60 m/s.
10
In order to find the depth of a well, you drop a stone into it and time its fall. It hits the water after falling for 1.5 s. The depth of the well is about
11 m
A car starts from rest and reaches 10 m/s in 5 seconds. The average acceleration of the car is
2.0 m/s^2
One inch is defined as 2.52 centimeters. The correct expression for a one-inch length, expressed in meters is...
2.54 x 10^-2 meters
A car is decelerating at the rate of 2 km/s^2. If its initial speed is 66 km/s, how long will it take the car to come to a complete stop?
33s
An iron robot falls from rest at a great height. Neglecting air resistance, what distance has it fallen in the first 3.5 seconds?
34.3 m/s
A 10 kg object dropped from a certain window strikes the ground in 4.0 s. Neglecting air resistance, a 5 kg object dropped from the same window strikes the ground in
4.0 s
For identical cannons identical projectiles and identical initial speeds, but different pointing angles, the maximum distance for its projectile is attained for the cannon which launches at
45 degrees above horizontal
In order to go from rest to 50 m/s in 10 s, a jet must be able to accelerate at
5 m/s
A certain parcel of real estate is sold for 5.0 Mega dollars. What is the correct scientific notation for this selling price?
5.0 x 10^6 dollars
A body travels at an initial speed of 2.5 m/s. Given a constant acceleration of 0.2 m/s^2, what is the speed of the body at time 25 seconds later?
7.5 m/s
A scout steps off a distance of 140 steps. If each step is 65 cm, what is the distance in meters?
91 m
______ is required to produce a change in either the magnitude (speed) or direction of velocity
A Force
The numerical factor 10^9 corresponds to what quantity?
A billion
Students often fail to include units with their answers. Science teachers say that units are important. Give an example of a situation where units are important.
A friend offers you two per mile to help pay for has on a trip
The object's __________ is its _________ with respect to a chosen reference point.
position; location
Science
An Ordering of the World Around Us
Translational
An example is a car traveling on a highway
Rotational
An example is the Earth's spin on its axis
Vibrational
An example is the back-and-forth movement of a pendulum or spring
In a laboratory on Earth, all the air is pumped from a large tube. A feather and a steel ball are simultaneously released from rest inside the tube. What happens next?
Both objects fall and hit the bottom at the same time
Motion
represents a continual change in an object's position
Angular momentum
rotational momentum of a spinning or orbiting object Examples include: a bicycle wheel, an atom, and a galaxy
If velocity is increasing, the acceleration is in the ________ direction as the velocity
same
A car driver takes Turn 1 at Daytona International Speedway at a steady 120 mph all the way through the turn. The radius of this turn is 1000 feet. Which statement is true?
Change of direction at constant speed means a change in velocity
When a scientist wants to strengthen a theory, she can make predictions of measurable events. The theory becomes stronger when...
she and other scientists observe and measure the events, and they find that the events agree with the prediction
John walks from point A to points B and then back to point A along the straight line Find the distance he made
Distance = 50 m + 50 m = 100 m
position-versus-time displacement-versus-time
slope = instantaneous velocity slope is negative between 50 s and 60 s, so car moves in opposite direction
A quantity is a measure of how the distance traveled changes with time is
speed
In physics, change in velocity means change in the object's...
speed or direction of motion
What is the order of the scientific method
Hypothesis (theory) -> observation (experiments) -> generalization
The motion of a falling object is commonly investigated with the aid of a
stroboscope
The velocity of a body is graphed as a function of time. The slope of the graph at any point may be identified with
Instantaneous acceleration
Suppose a graph of position versus time is constructed. The slope of the graph at any point may be identified with
Instantaneous velocity
Even a decrease in velocity (a slowing down)
Is acceleration
Acceleration is a vector quantity
It has magnitude and direction.
Uniform (constant) Acceleration
It occurs whenever there is a constant force acting on an object. The acceleration (as a vector) does not change as the motion proceeds (its magnitude and direction are constant).
John walks from point A to points B and then back to point A along the straight line Find the magnitude and direction of his displacement vector
John finished his walk at the same position he started it. Therefore, xf = xi , and /_\x = xf - xi = 0 m
In Mechanics, three fundamental quantities are used
Length Mass Time (All other quantities in mechanics can be expressed in terms of the three fundamental quantities.)
You travel 2640 feet in thirty seconds while in a 65 mi/hr zone. (There are 5280 ft in one mi). Your average speed is
Less than the speed limit
Instantaneous acceleration
the acceleration at that precise instant in time the rate at which velocity is changing at a given instant in time.
the magnitude of acceleration is highest at
Region c
Standardized systems of units SI US
SI - Systéme International US Customary System
The same physical principles that govern our everyday experiences also govern...
the entire universe
Physics is considered the "fundamental science" because
the ideas and concepts of physics are an important part of the foundation of other sciences
Which of the following quantities relating to motion is not a vector?
Speed
The diagram shows the positions at 0.10-sec intervals of a ball moving left to right. Is the ball accelerated?
The ball moves an equal distance during each 0.10-sec interval, so the speed does not change. Since the ball moves in a straight line at a constant speed, it is not accelerated
Velocity versus Time Graph Velocity fastest at
The graph is steepest and has the greatest slope between 2 s and 4 s, the velocity is changing fastest during this interval making the acceleration the greatest.
Two projectiles are launched at 50 degrees above horizontal but with different initial speeds. Which of the following mmust be true while the porjectiles are in the air? (ignore air resistance)
The horizontal accelerations of both projectiles are the same; zero
What does a car's speedometer measure?
The speedometer tells us how fast we are going at a given instant in time. The speedometer doesn't indicate direction, so it indicates instantaneous speed but not velocity.
Suppose a theory is used to make a prediction. A measurement is carried out to test the prediction. The measurement is found to have a value far larger than prediction. This means...
The theory might have correct elements but must be modified to account for some unforeseen influences
Velocity versus Time Graph Velocity constant at
The velocity is constant between 0 s and 2 s. The velocity is not changing during this interval, and the graph is flat, it has a slope of zero
Velocity versus Time Graph Does it ever go backward?
The velocity is decreasing between 4 s and 6 s, the velocity is still positive and in the same direction (it is not negative), so the car is not moving backward
A car goes around a curve at constant speed. Is the car's velocity changing?
Yes, At position A, the car has the velocity indicated by the arrow (vector) v1. At position B, the car has the velocity indicated by the arrow (vector) v2, with the same magnitude (speed) but a different direction
A ball is thrown straight up. It reaches its highest point and then falls back. What is the ball's velocity?
Zero
Which of the following represent the best explanation we currently have? a.) Einstein's Theory of Relativity b.) Newton's Law of Gravitation
a.) Einstein's theory built on Newton's and better describes observations since Newton's time.
Which of the following is a correct metric unit for volume? a.) liters b.) smidgens c.) drops d.) microns
a.) liters
A car starting from rest, accelerates to a velocity of 20 m/s due east in a time of 5 s.
a= 20m/s / 4m/s/s = 4m/s^2
A body whose velocity increases by a constant amount each second is exhibiting motion for which the ____________________ is constant.
acceleration
A quantity that is a measure of how the velocity of a body changes with time is
acceleration
Scalar quantities
are completely described by magnitude only
Units
are standards for measurement of physical quantities that need clear definitions to be useful
A car traveling at constant speed can...
change direction
Slope
change in vertical quantity divided by a change in horizontal quantity
The principal advantage of metric units over English units is that
conversions between units are easier
An object moving at 30 m/s has an acceleration of -2.0 m/s/h. Its speed
decreases very slowly
Speed
describes how fast an object changes its position (location). Speed is always some distance divided by some time.
Velocity
direction of motion and how fast the object is going [vector quantity]
If the velocity is constant, our bodies...
don't feel velocity
Which of the following units is not appropriate for measuring volume? a.) pint b.) liter c.) milliliter d.) cup e.) centimeter
e.) centimeter
For a ball bouncing from a wall, the wall exerts a _________ on the ball, causing the ball to change ___________.
force; direction
For the car to round the curve, friction between the wheels and the road exerts a _______ to change the car's _________.
force; direction
Point mass
has negligible dimension and the mass is concentrated at the point itself.
% error
is a measure of accuracy | experimental - theory | --------------------------- x 100% theory
% difference
is a measure of precision | experimental - theory | -------------------------------- x 100% | experimental - theory | / 2
Instantaneous velocity
is a vector quantity having: a size (magnitude) equal to the instantaneous speed at a given instant in time, and a direction equal to the direction of motion at that instant.
Precision
is associated with random errors and determines the degree of reproducibility or repeatability of experimentally measured value.
Displacement
is defined as the change in position during some time interval [Vector quantity] /_\x ≡ xf - xi
Accuracy
is related to systematic errors and determines how close our experimentally measured value is with respect to its true (table) value.
Distance
is the length of a path followed by a particle [Scalar quantity]
Which of the following is not an appropriate unit for measuring acceleration?
m/s
Vectors have both ...
magnitude and direction
density =
mass mass -------- = ---------------------- volume length*length*length
The development of physics concepts depends heavily on measurements because
measurements are needed to prove ideas true or false
What types of units can speed be
miles/hour meters/second kilometer/hour inches/minute
Vector quantities
need both magnitude (size or numerical value) and direction to completely describe them
The tip of the second hand of a clock moves in a circus of 20 cm circumference. in one minute the hand makes a complete revolution. Its average velocity over that time is ______ cm/s
o
Significant figures
of a number are those digits that are meaningful in determining its precision. The number of significant figures is the number of reliably known (or measured) digits in a number. Zeroes are sometimes written even though they are not significant (placeholders).
Rate
one quantity divided by another quantity.
If velocity is decreasing, the acceleration is in the _______ direction as the velocity
opposite
In motion diagram
the moving object is drawn at a sequence of equally spaced time intervals formed by imagining the stroboscope
Acceleration
the rate at which velocity changes. either a change in the object's speed or direction of motion. [Vector quantity]
Instantaneous speed
the speed at that precise instant in time. the rate at which distance is being covered at a given instant in time.
Electricity and Magnetism
the study of electric and magnetic forces and electric current
Mechanics
the study of forces and motion
Optics
the study of light
Nuclear physics
the study of nucleus of the atom
Atomic physics
the study of structure and behavior of atoms
Particle physics
the study of subatomic particles: quarks, etc.
Thermodynamics
the study of temperature, heat, and energy
Condensed matter physics
the study of the properties of matter in the solids and liquids states
The directions of the velocity and acceleration of an object which is thrown straight upward and then falls back down (ignore the effects of air resistance)
the velocity changes direction but the acceleration always stays the same
Average speed
total distance divided by total time It is the rate at which distance is covered over time
The acceleration of a body is given by the slope of a graph plotting
velocity versus time
Testing
will tell if the prediction is accurate
xi Xf
xi - initial position xf - final position