physics
The muzzle velocity of a bullet fired from a new rifle is 100 m/s. Neglecting air resistance, at the end of one second a bullet fired straight up into the air will have traveled a distance of
(100-5)m.
An apple weighs 1N. When the apple is held at rest above your head, the net force on the apple is
0 N
what is the weight of a 1-kilogram brick resting on a table
10 N
If a freely falling object were equipped with a speedometer, its speed reading would increase each second by about
10 m/s
The mass of a pet turtle that weighs 10 N is about
1kg
The greek mathematician Eratosthenes made measurements to show the size of
Earth
if the forces that act on a cannonball and the recoiling cannon from which it is fired are equal in magnitude, why do the cannonball and cannon have very different accelerations?
Remember F = ma, and note that the cannon has a much greater mass than the cannon ball, so the cannon accelerates less for the same force.
What relationship between the Sun and Earth did Copernicus formulate?
The Earth revolved in a circle about the Sun
What did Galileo discover about the amount of speed a ball gained each second when rolling down an inclined plane? What did this say about the ball's acceleration?
The ball had constant acceleration, so it gained the same speed every second.
What is the net force on a bag pulled down by gravity with a force of 18 N and pulled upward by a rope with a force of 18 N
The force is zero newtons
what is the net force on a cart that is puled to the right with 100 pounds of force to the left with 30 pounds of force
The net force is 70 pounds to the right
What is the net force of an object in either static or dynamic equilibrium?
The net force is zero
How does the magnitude of the vertical component of velocity for a ball tossed at an upward angle change as the ball travels upward? How about the horizontal component of velocity when air resistance is negligible?
The vertical component decreases in magnitude until it reaches the maximum height and then increases; the horizontal component is constant.
A 1000-kg automobile enters a freeway on-ramp at 20 m/s and accelerates uniformly up to 40 m/s in a time of 10 seconds. How far does the automobile travel during that time?
Vf = Vi+at 40 = 20+10a a = 2 m/s/s Vf^2 = Vi^2+2ax 1600 = 400 + 2(2)x 1200 = 4x x = 300m<---
When you stand at rest on a bathroom scale, how does your weight compare with the support force from the scale?
Your weight is equal in magnitude and opposite in direction to the support force from the scale
state newtons second law of motion
acceleration is proportional to net force and inversely proportional to mass
A fact in science is
an agreement between trained investigators
What exactly is meant by a freely falling object?
an object in free fall falls under gravity alone with no friction.
Technology is a tool for
applying scientific discoveries
if you toss a coin straight upward while in a train moving at constant velocity, the coin will land
as if you were at rest
Phil Physiker standing at the edge of a cliff throws one ball straight up and the other ball straight down, both with the same speed. Neglecting air resistance, which ball hits the ground below with a greater speed.
neither, they both hit with the same speed
since an object weighs less on the surface of the moon than on earths surface, does it have less inertia on the moons surface? (y/n)
no
The force that causes Earth to orbit the Sun is dur to gravity, while the force needed to keep Earth moving as it circles the Sun is
no force at all
why does a heavy parachutist fall faster than a lighter parachutist who wears a parachute of the same size?
terminal speed must be higher to make air drag equal to the gravity force for a heavier person
what is the acceleration of a falling object that has reached its terminal velocity
the acceleration is 0
how does the direction of acceleration compare with the direction of the net force that produces it?
the acceleration is in the direction of the net force
if two objects the same size move through the air at different speeds, which encounters the greater air resistance?
the faster object encounters more air resistance
what two principal factors affect the force of air resistance on a falling object
the force depends mostly on frontal area and speed
A bullet is dropped into a river from a very high bridge at the same time another bullet is fired straight downward from a rifle. Neglecting air resistance, the acceleration just before striking the water is
the same for each bullet
What is the speed acquired by a freely falling object 5s after being dropped from a rest position? what is the speed 6s after?
the speed is 50 m/s after 5s; 60 m/s after 6s.
When you are standing in the aisle of a bus, the driver suddenly makes a left turn. You lurch to the right due to
the tendency to keep moving forward
The synthesis of a large collection of information that contains well tested and verified hypotheses about certain aspects of the world is known as a scientific
theory
Earth continually moves about 30km/s through space, which means the wall you stand next to also moves at 30 km/s. When you jump vertically the wall downt slam into you because
you're moving horizontally just as fast as the wall
The net force on any object in equilibrium is
zero
State the equilibrium rule for forces in a symbolic notation
ΣF = 0
What is the acceleration of a car that maintains a constant velocity of 100 km/h for 10 s?
0 km/h*s
A mosquito flying at 3 m/s that encounters a breeze blowing at 3 m/s in the opposite direction has a speed of
0 m/s
What is the net force when a pair of 5-N forces simultaneously act in the same direction on an object?
10 N
when a ball thrown straight upwards reaches the very top of its path, its acceleration is
10 m/s^2
what is the net force acting on a 1-kg ball in free fall
10.0 N
a river 100m wide flows due south at 1 m/s. A boat travels 1 m/s relative to the water is pointed east as it crosses from the west bank. The boat reaches the east bank
100 m further south
A 1-kg mass at the earths surface weighs
10N
The distance between the Earth and the Su is approximately
110 Sun diameters
While you are in a bus that moves at 100 km/h you walk from the back to the front at 10 km/h. What is your speed relative to the road outside
110 km/h
An object released from rest on another planet requires one second to fall a distance of 6 meters. What is the acceleration due to gravity on this planet?
12 m/s^2
Calculate the acceleration of a 300000-kg jumbo jet just before takeoff when the thrust on the aircraft is 120000N . (Acceleration: a=Fnet/m)
120,000/300,000 =0.40 m/s^2
What is the speed over the ground of an airplane flying at 100 km/h relative tot eha ir caught in a 100-km/h right-angle crosswind?
141 km/h
Consider a book that weighs 15 N at rest on a flat table. How many newtons of support force does the table exert on the book?
15 N up
If a stone falls to the bottom of a mineshaft in 6 seconds, then the depth of the shaft is about
180 m
an apple at rest weighs 1N. The net force on the apple when it is in free fall is
1N
The time it takes a projectile fired straight up at 10m/s to reach the top of its path is about
1s
if you pull horizontally on a crate with a force of 200 N, it slides across the floor in dynamic equilibrium. How much friction is acting on the crate?
200 N
A car has a mass of 1000 kg and accelerates at 2 m/s^2. What net force is exerted on the car?
2000N
How much support force acts on a 200-N girl standing on a weighing scale?
200N
The total time it takes a projectile fired straight up at 10m/s to reach the top of its path and return to its starting point is about
2s
What is the average speed in kelometers per hour of a horse that gallops a distance of 15 km in a time of 30 mins?
30 km/h
A 2000-kg car experiences a braking force of 10,000 N and skids to a stop in 6 seconds. The speed of the car just before the brakes were applied was
30 m/s
a grocery bag can withstand 300N of force before it rips apart. How many kilograms of apples can it safely hold?
30.0 Kg
An astronaut on another planet drops a 1-kg rock from rest and finds that it falls a vertical distance of 2.5 meters in one second. On this planet, the rick has a weight of
5 N
A humming bird flying at 4 km/h that gets caught in a 3-km/h crosswind has a resultant speed of about
5 km/h
The resultant of a 40-N force at right angles to a 30-N force is
50 N
calculate the weight in newtons of a person having a mass of 56kg.
560 N
if you throw a stone horizontally from the top of a cliff, one second after leaving your hand its vertical distance below the top of the cliff is
5m
A mosquito flying at 3 m/s that encounters a breeze blowing at 3 m/s in the same direction has a speed of
6 m/s
Why do we say that force is a vector of quantity?
A force has a magnitude and direction
A ball is thrown vertically into the air. Because of air resistance, its speed when it returns to its starting level compared with its initial speed is A. less B. the same C. more
A. Less
How does acceleration depend on mass?
Acceleration is inversely proportional to mass
What does it mean to say something is in mechanical equilibrium?
An object in mechanical equilibrium experiences a zero net force
The amount of force needed to sustain motion of a rock in outer space is A. a force les than its weight if friction is absent B. a force = to its weight C. none of these
C. none of these
An object in mechanical equilibrium is an object A. having no changes in velocity B. at rest C. moving with constant velocity D. all of the above
D
Recall Galileo's Leaning Tower experiment. With negligible air resistance, a heavy and light object fall A. with equal accelerations. B.to the ground in equal times. C. with the same increases in speed. D. all of the above
D. all of the above
A hockey puck is set in motion across a frozen pond. If ice friction and air resistance are neglected, the force required to keep the puck sliding at constant velocity is? A. equal to its weight B. equal to its weight divided by its mass C. equal to its mass times its weight D. none of the above
D. none of the above
A Volkswagen Bug and a Volvo truck have a head-on collision. What statement is true? A. The greater force acts on the Volvo truck. B. Both forces are identical. C. The greater force acts on the Volkswagen Bug. D. The magnitudes of both forces are the same.
D. the magnitudes of both forces are the same
What are the units for force?
Force can be expressed in Newtons (N) or pounds (lbs)
what relationship between distance traveled at time did Galileo discover for freely falling objects released from rest?
Galileo discovered that distance increased as the time squared.
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.
What did Galileo discover about moving bodies and force in his experiments with inclined planes?
In the absence of a retarding force, a body will keep moving a constant speed in a straight line forever.
When an object is thrown upward, how much speed does it lose each second (ignoring air resistance) ?
It loses 10 m/s of speed each second until it reaches the high point, then it gains 10 m/s each second.
What two classes of motion did Aristotle advocate
Natural motion and violent motion
The unit of mass is the kilogram, ad the unit of weight is the
Newton
How does Newton's first law of motion relate to Galileo's concept of inertia?
Newton refined Galileo's concept of inertia and made it his first law of motion.
Which of Newtons laws does the equilibrium rule illustrate?
Newtons first law
What did Copernicus say about the motion of the Sun?
The Sun is stationary and Earth circles it
if the mass of a sliding block is tripled while a constant net voce is applied, by how much does the acceleration change?
The acceleration is reduced to 1/3 of its original value
According tot he parallelogram rule, what quantity is represented by the diagonal of a constructed parallelogram?
The diagonal is the resultant, or sum, of two vectors.
If you push on a crate with horizontal force of 100 N and it slides at constant velocity, what is the magnitude and direction of the frictional force acting on the crate?
The frictional force on the crate is 100 N opposite the direction of motion.
What is th enet force that acts on a 10-N falling object when it encounters 4N of air resistance? when it encounters 10 N of air resistance?
The net forces are 6 N and 0 N, respectively.
What is the resultant of a pair of one pound forces at right angles to eachother?
The resultant is a force of 1.41 pounds in a direction bisecting the 90-degree between the two vectors
What relationship did Galileo discover about a ball's acceleration and the steepness of an incline? What acceleration occurs when the plane is vertical?
The steeper the incline, the greater the acceleration. On a vertical incline, the ball is in free fall.
What concept was not understood in the 16th century when people couldn't conceive of a moving Earth?
They did not understand inertia
Henry Heavyweight weighs 1200N and stands on a pair of bathroom scales so that one scale reads twice as much as the other.
W1,W2 = 800,400 N
Stand next to a wall that travels at 30 km/s relative to the Sun. With your feet on the ground, you also travel at the same 30 km/s. Do you maintain this speed when your feet leave the ground? What concept supports your answer?
When you jump, you continue to move at 30 km/s due to your inertia.
A car takes 15s to go from v=0m/s to v = 30m/s at constant acceleration. (If you wish to find the distance traveled using the equation d=1/2at2, what value should you use for a?)
a = 2.0 m/s^2
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
In science, a theory is
a synthesis of a large body of well tested knowledge
A theory in science is
a synthesis of well-tested ideas
As a ball falls, the action force is the Earths pull on the ball. The reaction force is
balls pull on earth
A ball rolls off the edge of a table at the same time another ball drops vertically from the same table. the ball to hit the floor first is the
both hit at the same time
The easiest way for you to measure the distance between the Earth and the moon is to place in your line of sight to the moon a
coin
Suzie Skydiver jumps from a high-flying plane. As her velocity of fall increases, her acceleration
decreases
Whirl a rock at the end of a string and it follows a circular patch. if the string breaks, the tendency of the rock is to
follow a straight line path
A player hits a ball with a bat. if action is the force of the bat against the ball, reaction is the
force that the ball exerts on the bat
If an object falling freely were somehow equipped with an odometer to measure the distance it travels, then the amount of distance it travels each succeeding second would be
greater than the second before
When Nellie Newton hangs by the ends of a rope draped over a large pulley, the tension in each supporting vertical strand is
half her weight
a skydivers terminal velocity will be greatest if she falls
head first
In science, an educated guess is a
hypothesis
as a skydiver gains speed in falling through the air, air resistance
increases
when you flick a card from beneath a coin that hardly moves, youre illustrating
inertia
what kind of speed is registered by an automobile speedometer
instantaneous speed
air resistance on a parachutist at terminal speed
is greater for a heavier person
A bird sitting in a tree is traveling at 30 km/s relative to the faraway sun. When the bird drops to the ground below, does it still move 30 km/s, or does this speed become zero?
it continues to move at 30 km/s relative to the sun, but it has a speed of 0 relative to the ground
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
What is the distance fallen for a freely falling object 1s after being dropped from a rest position? What is the distance for a 4s drop?
it falls 5m in 1s and 80m in 4 s
if a car is moving at 90km/h and it rounds a corner, also at 90 km/h, does it maintain a constant speed? A constant velocity?
it maintains constant speed, but does not maintain constant velocity.
Galileo taught us that if you roll a ball along a level surface it will
keep rolling if friction is absent
Susie Small finds that she weighs 350 N. Calculate her mass
m=35 kg
In science, facts
may change
Of the sciences known as physics, chemistry, and biology, the most basic is
physics
inertia is defined as a
property of matter
As soon as a bowling ball rolls off the edge of a table its horizontal component of velocity
remains constant
Monkey Mo hangs from the middle of a horizontal rope. Tension in the rope is greatest if the rope
sags very little
shake something to and fro your you're measuring its what? lift it against gravity and you're measuring its what?
shaking measures mass, whereas lifting measures weight
when no forces act on moving objects their paths are normally
straight lines
A force of gravity pulls downward on a book on a table. What force prevents the book from accelerating downward?
support
as you increase your push on a stationary crate, will friction on the crate increase also?
the friction force increases and is opposite in direction to your push
when you push horizontally on a crate that doesn't slide on a level floor, how great is the force of friction on the crate?
the friction force is equal and opposite to your push
A feather and a coin will have equal accelerations when falling in a vacuum because
the ratio of both the feather's and the coin's weight to mass is the same.
a 1-kg stone and a 10-kg stone have the same acceleration in a free fall because
the ratio of weight to mass is the same for each
A ball is thrown upwards and returns to the same location. Compared with its initial speed its speed when it returns is about
the same
Compared to the mass of an apple on earth, the mass of the apple on the moon is
the same
Whenever a net force acts on an object, there is a change in the objects
velocity
what is the main difference between speed and velocity
velocity includes a direction, but speed does not.
with caries with location, mass or weight?
weight
A scientific hypothesis deemed valid must have a test for proving it
wrong
A scientific hypothesis may turn out to be right or it may turn out to be wrong. If it is a valid hypothesis, there must be a test for proving it..? (right or wrong)
wrong
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 = 0
Once the crate is sliding, how hard do you push to keep it moving at constant velocity
you push with a force equal to and opposite the dynamic friction force
