PH218 Exam 1
What is a force?
interaction between two objects: push or pull.
Dynamic equilibrium
something is moving at a constant velocity
displacement
the shortest distance between 2 points, and whose direction points from start to end point.
Newton's 1st Law
(Law of Inertia) an object in motion tends to stay in motion & an object at rest stays at rest unless acted upon by an outside force.
Friction
A force that opposes motion
A book weighs 10 N. The net force on the book when it is at rest in your hand is A) 0 N B) 1 N C) 10 N D) 98 N E) none of these
A) 0 N
A car has a mass of 1000 kg and accelerates at 2 m/s/s. What is the magnitude of the force exerted on the car? A) 2000 N B) 500 N C) 1000 N D) 1500 N E) None of these
A) 2000 N
A person is attracted toward the center if the Earth by a 120 pound gravitational force. The force of attraction of the Earth toward the person is A) much larger than 120 lb B) much less than 120 lb C) 120 lb
C) 120 lb
The weight of 0.6 kg of salami is about... A) 0.06 N B) 60 N C) 6.0 N D) 600 N
C) 6.0 N
A very massive object A and a less massive object B move toward each other under the influence of gravitation. Which force, if either, is greater? A) The force on A B) The force on B C) Both forces are the same
C) Both forces are the same
Acceleration
Change in velocity divided by the time it takes for the change to occur
A 300-kg bear grasping a vertical tree slides down at constant velocity. The friction force between the tree and the bear is.. A) 30 N B) 300 N C) More than 3000 N D) 3000 N
D) 3000 N
An object is pulled northward with a force of 10 N and southward with a force of 15 N. The magnitude of the net force on the object is.. A) 15 N B) 10 N C) 0 N D) 5 N E) None of these
D) 5 N
A car accelerates from rest at 3 m/s squared. What is its speed 3s after the car starts moving? A) 6 m/s B) 3 m/s C) 1 m/s D) 9 m/s
D) 9 m/s
A kilogram is a measure of an object's.. A) Gravity B) Weight C) Force D) Mass E) Center of mass
D) Mass
The kg is a unit of A) velocity B) density C) weight D) mass E) acceleration
D) mass
What happens during orbit
The object in orbit is constantly falling toward the earth, but it is moving forward fast enough that it keeps missing.
Terminal speed
The speed at which the acceleration of a falling object terminates because air resistance balances its weight.
What is inertia
The tendency of an object to resist a change in motion
Aristotles theory of motion
believe that forces caused motion
Two basic types of forces
contact and non-contact
The distance that an object falls from rest can be found using the equation:
d = ½(-10 m/s2)t2
distance equation
d= df-di
Speed
distance/time
Galileo's ideas on motion
forces caused changes in motion
Static equilibrium
objects at rest
terminal velocity
terminal speed in a given direction (often downward)
The speed from which object falls from rest can be found using the equation:
vf = (-10 m/s2)t
Freefall
when the only force acting on an object is gravity
Newton's 2nd Law of Motion
The acceleration of an object depends on the mass of the object and the amount of force applied.
What is the acceleration of an airplane that maintains a constant velocity of 25 mi/hr for 1/2 hr? A) 0 B) 12.5 mi/hr squared C) 50 mi/hr Squared D) 60 mi/hr squared
A) 0
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) 0 N B) the mass of the puck multiplied by 10 m/s/s C) the weight of the puck divided by the mass of the puck D) Equal to the weight of the puck E) None of these
A) 0 N
If a freely falling object were somehow equipped with a speedometer, its speed reading would increase each second by about.. A) 10 m/s B) 15 m/s C) 5 m/s D) a variable amount E) depends on its initial speed
A) 10 m/s
Disregarding air resistance, objects fall at constant... A) Acceleration B) distances each successive second C) Velocity D) Speed
A) Acceleration
The scientist to first introduce the concept of inertia was.. A) Galileo B) Newton C) Aristotle D) Copernicus
A) Galileo
Two objects move toward each other because of gravity. As the objects get closer and closer, the acceleration of each.. A) Increase B) Decreases C) Remains constant
A) Increase
If an object's mass is decreasing while a constant force is applied to the object, the acceleration... A) Increases B) Decreases C) Remains the same
A) Increases
A force is a vector quantity because it has both.. A) magnitude and direction B) action and reaction counterparts C) mass and acceleration
A) Magnitude and direction
In what case would you have the largest mass of gold? If your chunk of gold weighed 1 N on the... A) Moon B) Planet Jupiter C) Earth
A) Moon
A rock is thrown upward at 50 degrees with respect to the horizontal. As it rises, its horizontal component of velocity.. A) Remains unchanged B) Decreases C) Increases
A) Remains unchanged
Compared with the mass of a certain object on Earth, the mass of the same object on the Moon is.. A) The same B) Less C) More
A) The same
A bullet is dropped into a river from a very high bridge. At the same time, another bullet is fired from a gun, straight down towards the water. Neglecting air resistance, the acceleration just before striking the water.. A) is the same for each bullet B) is greater for the dropped bullet C) is greater for the fired bullets D) depends on how high they started E) None of these
A) is the same for each bullet
When you stand on a bathroom scale in an elevator that is moving at a constant velocity downward, your weight, as read from the scale A) remains the same as when you are at rest B) is greater than when you are at rest C) is less than when you are at rest
A) remains the same as when you are at rest
Which of the following is a vector quantity? A) weight B) volume C) speed D) distance E) Mass
A) weight
A push on a 1-kg brick accelerates the brick. Neglecting friction, to equally accelerate a 10-kg brick, one would have to push with.. A) One-tenth the amount of force B) 10 times as much force C) Just as much force D) 100 times as much force E) None of these
B) 10 times as much force
A rock is thrown vertically into the air. At the very top of its trajectory the net force on it is.. A) less tha its weight B) its weight C) more than its weight
B) Its weight
Strange as it may seem, it is just as hard to accelerate a car on the Moon as it is to accelerate the same car on Earth. This is because the... A) Weight of the car is independent of gravity B) Mass of the car is independent of gravity C) A car is much more easily accelerated on the Moon than on the Earth
B) Mass of the car is independent of gravity
A package falls off a truck that is moving at 30 m/s. Neglecting air resistance, the horizontal speed of the package just before it hits the ground is.. A) less than 30 m/s but larger than zero B) about 30 m/s C) more than 30 m/s D) zero E) more information needed for an estimate
B) about 30 m/s
An archer shoots an arrow. Consider the action force to be the bowstring against the arrow. The reaction to this force is the.. A) air resistance against the bow B) arrow's push against the bowstring C) grip if the archer's hand on the bow D) friction of the ground against the archer's feet E) weight of the arrow
B) arrow's push against the bowstring
What keeps Earth moving? A) actually, it isn't moving B) it's inertia C) its accelerating D) gravity E) solar energy
B) its inertia
Astronauts in orbit around the Earth feel weightless because A) there is no gravity out there B) they are in "free fall" around the earth C) they are moving with constant velocity D) there are no forces at all acting on them E) the gravitational pull from the moon and other planets holds them up
B) they are in "free fall" around the earth
The force needed to maintain an object at constant speed in outer space (far from all outside influences) is equal to A) the weight of the object divided by its mass B) zero newtons C) the weight of the object D) the push force from the object E) none of these
B) zero newtons
A heavy object and a light object are dropped at the same from rest in a vacuum. The heavier object reaches the ground A) sooner than the lighter object B) later than the lighter object C) at the same time as the lighter object
C) at the same time as the lighter object
A player catches a ball. Consider the action force to be the impact of the ball against the player's glove. The reaction to this force is the... A) muscular effort in the player's arms B) Player's grip on the glove C) force the glove exerts on the ball D) friction of the ground against the player's shoes E) None of these
C) force the glove exerts on the ball
Your mass is A) a measure of the space you take up B) the gravitational attraction between you and the Earth C) how much matter you are made of D) two of these E) none of these
C) how much matter you are made of
A thrown baseball hits the windshield of a parked car and shatters it. The impact force is A) greater on the car windshield B) greater on the baseball C) the same for both D) there's not enough information given to tell
C) the same for both
What happens to the weight, mass, and inertia of a jug of water when it is taken to the moon, where gravity is less? A) weight decreases, mass stays the same, and inertia increases B) weight decreases, mass stays the same, and inertia decreases C) weight decreases, mass stays the same and inertia stays the same D) all three decrease
C) weight decreases, mass stays the same and inertia stays the same
Suppose a particle is being accelerated through space by a 10-N force. Suddenly the particle encounters a second force of 10 N in the opposite direction of the first force. The Particle with both forces acting on it.. A) Theoretically tends to accelerate toward the speed of light B) is brought to a rapid halt C) Decelerates gradually to a halt D) Continues at the speed it had when it encountered the second force. E) None of these
D) Continues at the speed it had when it encountered the second force
Which of the following is a scientific is hypothesis? A) Cats make better pets than fish B) There are parts of the universe that will never be found by man C) Matter is filled with undetectable particles D) People get colds due to becoming chilled after swimming
D) People get colds due to becoming chilled after swimming
According to Newton, wehn you double the distance between an object and the earth A) it increases the gravitational force between them to 2 times its original value B) it increases the gravitational force between them 4 times its original value C) it reduces the gravitational force between them to 1/16th of its original value D) it reduces the gravitational force between them to 1/4th of its original value E) it reduces the gravitational force between them to 1/2 of its original value
D) it reduces the gravitational force between them to 1/4th of its original value
In what kind of path would planets move if no force at all acted on them? A) they would just continue in their present orbits B) they have larger elliptical orbits C) they would travel in arcs, like thrown baseballs D) they would travel in straight lines at constant speed E) they would travel in straight lines with accelerations of 10 m/s squared
D) they would travel in straight lines at constant speed
Disregarding air drag, how fast must you toss a ball straight upward in order to remain in the air for a total time of 2s? A) 7.5 m/s B) 20 m/s C) 5 m/s D) 15 m/s E) 10 m/s
E) 10 m/s
What prevents satelites such as the space shuttle from falling? A) air pushing upward B) gravity C) the pull of the moon and other planets D) the pull of the sun E) Nothing; they continually fall around the Earth
E) Nothing; they continually fall around the Earth
A frosty cold mug of root beers is given a shove and released so that it slides across the tabletop and comes to rest in front of you. Aristotle's would say that the mug stopped because A) an object tends to return to its natural position B) of its inertia C) of gravity D) of friction E) an object must have a force on it in order to move
E) an object must have a force on it in order to move
Newton's Law of Universal Gravitation
Every object with mass attracts every other object with mass, with a force that is proportional to the masses and inversely proportional to the distance between them squared.
Equation for Newton's second law
Fnet=ma
Newtons 3rd Law
For every action force there is an equal and opposite reaction force
Velocity
Speed+direction
