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Level 73

Linear Momentum & Collisions


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Describe momentum
the product of mass times velocity
p = mv
Calculate the Momentum of an Object When Given Mass and Velocity
kg * m/s
What are the units of momentum?
kg * m/s^2
What are the units of force? Long and short version please!
kg * m^2/s^2
What are the units of work and energy? Long and short version please!
What does momentum allow for?
-the fundamental expression of Newton's second law
Fnet = Δp/Δt
What is the relationship between Fnet, Δp, and Δt?
Describe this relationship in words
Fnet tells you the rate of change of the momentum over time
the momentum over time
Therefore, if you are applying a net force, what are you changing?
because it assumes that mass is constant
Why is Fnet = ma a special case of Fnet = Δp/Δt?
Fnet = Δp/Δt = Δmv/Δt = mΔv/Δt = ma
If we assume that mass is constant, what is Δp/Δt equal to?
What if mass is not constant?
-examination requires calculus so we won't bother with it!
I = (Fav)(Δt)
What is impulse equal to?
What does it describe?
a Change in momentum
Conservative
Force of gravity
What is the definition of linear momentum?
the product of the mass m and the velocity of an object
What specifically is constant LINEAR momentum?
the object of mass m that is moving in a straight line with a velocity v
yes
mushroom have pores??
Therefore what does it have?
both a magnitude and a direction
a vector
If velocity is a vector, what is momentum?
a positive momentum
In order to increase the momentum from a negative value to zero, what is it necessary to add?
Describe this law
the net force is the rate of Change of momentum with time
When mass is constant
In what case does Fnet = ma?
the force required is greater in the hail
Is the force required to hold an umbrella during hail the same as, more than, or less than the force required in the rain?
Why?
because both person a and B cover the same angle in the same time
conserved
If the net force acting on an object is zero, is its momentum conserved or not conserved?
Action-reaction pairs
Two forces that have equal strengths but opposite directions are called _______.
zero
ΔH° for a pure element is _______
the sum of the external forces acting on it
Therefore, what is the sum of the net force acting on a system?
no effect
To summarize, what effect do internal forces have on the net momentum of a system?
the net momentum is conserved
If the net external force acting on a system is zero, what about the momentum?
What do these statements apply to?
the net momentum of a system
What is a collision?
a situation in which two objects strike one another in which the net external force is zero or negligibly small
the momentum of a system is conserved
What happens to the momentum of a system during a collision?
What about kinetic energy?
-most or even all of a system's kinetic energy may be converted to other forms during a collision
elastic collisions
objects bounce off each other
When KEf KEi
When are conditions said to be elastic?
When are conditions said to be inelastic?
When KEf is not equal to KEi
it decreases
What typically occurs to KE?
-sound, heat and deformation
Due to losses associated with...?
If the collision sets off an explosion
Provide an example of when KE may increase as a result of a collision?
momentum of a system is conserved
To summarize, describe conditions of inelastic conditions in terms of momentum and kinetic energy
What is a completely inelastic collision?
a collisions where objects stick together afterwards
the maximum amount of kinetic energy is lost
In a completely inelastic collision, what occurs to the KE?
final velocity = 1/2 initial velocity
What is the relationship between initial velocity and final velocity in a system that has just experienced an inelastic collision?
the details of the collision itself
Using momentum to evaluate a collision between two objects allows us to bypass what?
using external forces
If you want to change the momentum of two objects involved in a collision, how must you do so?
for multi-object system with unknown internal forces
For what type of conditions is momentum most useful for?
are equal in magnitude and opposite in direction
If the two people standing on ice push off of each other, what is the relationship between their momenta?
When is the momentum of a system conserved?
When the net external force on a system is equal to zero
When is mechanical energy conserved?
When work non-conservative is equal to zero
KE and PE
What are the two types of mechanical energy that we work with the most?
Elastic
Ability of matter to return to its original dimension or shape after deformation.
internal
Are forces internal, external, or both during elastic collisions?
KE initial = KE final
If forces are conservative, what is the relationship between KE initial and KE final?
KE
Before collision, will the energy of the system be predominantly KE or PE?
PE
During the collision?
What is the potential energy of gravity equal to during elastic collisions? Why?
the potential energy of Gravity is equal to zero because collisions typically occur on a flat surface
no
is there any acceleration after terminal velocity has been reached?
Where does the energy go?
energy is lost to the environment
the degree to which KE is lost
What is the difference between partially inelastic conditions and completely inelastic collisions?
What event of importance occurs during completely inelastic conditions?
so much energy is lost that objects will not separate after the collision
internal and conservative
Therefore, how would you describe the forces that act during an elastic collision?
Why not?
because each different conservative force has a different expression for potential energy
internal and non-conservative
Therefore, how would you describe the forces that act during an inelastic collision?
KE final > KE initial
Therefore, what is the relationship between KE final and KE initial?
positive non-conservative work
What must have taken place?
Where did this work come from?
the chemical energy from the persons
What then was added to the system?
mechanical energy in the form of KE
no it is not
If a ball is free falling under the influence of gravity, is momentum conserved?
momentum will be conserved
What will be the effect of momentum conservation if Earth is added to the system?
What is the center of mass of an object?
the only part of an extended object that obeys Point particle physics
What is an extended object?
an object that has size and Shape
linear/translational motion
What type of motion does the COM exhibit?
Rotational Motion
Forces applied to an object cause the object to rotate around a fixed point (fulcrum)
geometric center
What is the midpoint of an object referred to as?
Is the geometric center the COM for asymmetrical objects?
-no, the COM is not likely to be the midpoint/geometric center of an object that is asymmetric
figure out how much mass is at each coordinate
When objects sit in a 2D plane, what is the first step to calculating the COM?
Then?
pick one object to set as the origin
decreased
During this collision, the ME of the A + B system is...?
Increases
As temperature increases, the vapor pressure of a liquid _______.
What will happen to his mechanical energy?
-since friction acts, ME is removed to heat
What will happen to the size of his momentum?
increases (since it is dependent on mv and Bob is speeding up)
stays the same
if you changed the mass of the pendulum bob, how would the period be affected
while Bob was in the air
If we were to compare an equal height drop while Bob was on the hill vs. through the air, in which case would the increase in speed be greater?
the momentum of the keys increases as they fall because a net force acts on them
If you drop your keys, their momentum increases as they fall. Why is the momentum of the keys not conserved? Does this mean that the momentum of the universe increases as the keys fall? Explain
When a heavy object and a light object collide they exert equal and opposite forces on one another
Crash statistics show that is safer to be riding in a heavy car in an accident than in a light car. Explain in terms of physical properties?
When the objects have momenta of equal magnitude prior to the collision
In what scenario can two objects on a horizontal frictionless surface have a collision in which all the initial KE of the system is lost?
the KE of the bullet is much greater than the gun
At the instant a bullet is fired from a gun, the bullet and the gun have equal and opposite momenta. Which object--the bullet or the gun--has the greater KE? Explain.
the rubber bullet is more likely to knock the block over
A block of wood is struck by a bullet. Is the block more likely to be knocked over if the bullet is metal and embeds itself in the wood, or if the bullet is ru…
Parabolic Path
A plane, flying horizontally, releases a bomb, which explodes before hitting the ground. Neglecting air resistance, the center of mass of the bomb fragments, just after the explosion moves along a _______
Magnitude Impulse
Two equal mass balls, A and B, are dropped from the same height, and rebound off the floor. The A ball rebounds to a higher position. The A ball is subjected to the greater…
Momentum (Kinetic Energy)
The product of an object's mass and velocity is equal to _______
External Forces
Kinetic energy is never conserved for a perfectly inelastic collision free of _______
Center of mass
same as center of gravity
Momentum Change
A small object collides with a large object and sticks. Both objects experience the same magnitude of _______
Some Point
For an object on the surface of the earth, the center gravity and the center of mass are the _______
the same
if take off and landing heights of a trajectory of a projectile are the same, then the time from ground to apex should be _______ the time from apex to ground
momentum
(p) vector quantity describing the quantity of motion or inertia in motion. Recognizes that both mass and velocity have a part in the motion of an object and is proportional to both (is zero …
the time of impact
A baseball catcher wears a glove rather than just using bare hands to catch a pitched baseball because the force on the catcher's hand is reduced because the glove increases __
Decreases
A freight car moves along a frictionless level railroad
They are the Same
A golf ball moving east at a speed of…
Constant
Satellite speed
Balance Point
The center of gravity of an object may be thought of as the __
Backwards
A 100-kg football linebacker moving at 2 m/s tackles head-on an 80-kg halfback running 3 m/s. Neglecting the effects due to digging in of cleats, the halfback will drive the linebacker __
impulse
a large change in momentum over a short period of time
Same Average Force
A small car meshes with a large truck in a head-on collision. The small car and large truck experience the __
vector
a displacement distinguished by magnitude and direction but not by location.
Acceleration due to gravity
9.8 m/s/s or m/s^2 in the metric system
Doubled
If the mass of a moving object could be doubled, the inertia would be __
4x as great
compared to the inertia of a 1-kg mass, the inertia of a 4kg mass would be __
weight and momentum
a copper coin is resting on a piece of cardboard is placed on a beaker as shown in the diagram below when the cardboard is rapidly removed, the coin drops into the beaker. The proper…
Decrease
As the mass of an object decreases, its inertia will __
greater momentum
A 5N ball and a 10N ball are released simultaneously from a point 50m above the surface of the Earth. Neglecting air resistance, which statement is true? at the end of 3s of free-fall.…
More Momentum
In the diagram below, a .4kg steel sphere and a .1kg wooden sphere are located 2.0m above the ground. Both spheres are allowed to fall from rest. Best statement when they fell 1m: Both sph…