Notes 21- CP Physics Student Notes: Chapter 7 -- Momentum
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In Physics, Momentum, ________, is defined as the product of an object’s Mass times its Velocity.
The equation for Momentum is...
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The unit used to measure p is ________________, which is just the unit of mass (kg) times the unit
of velocity (m/s).
Momentum is a __V_________________ quantity, meaning that it has both a
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__M_________________ and a __D_____________________.
The direction of momentum is
ALWAYS the same as the direction of the velocity. Because of this, Momentum can be either
__P________________ or __N__________________.
Ex. 1: What is the momentum of a 70 kg soccer player running with a velocity of 5 m/s?
Ex. 2: What is the momentum of a 5,000 kg truck driving with a velocity of -10 m/s?
Ex. 3: (Extension of Ex. 2) If a 2,000 kg car is driving so that it has the same Momentum as the truck,
what is its velocity?
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Isaac Newton defined Momentum as the “__Q______________________ of __M______________.”
When an object’s motion changes, we will say that its Momentum changes. To determine the
change in an object’s momentum, we use the following equation:
Ex. 4: A 200 kg motorcycle accelerates from rest to a final velocity of 20 m/s. What is its change in
Momentum?
Ex. 5: An 80 kg running back has an initial velocity of 6 m/s and experiences a change in his momentum
equal to -400 kg*m/s. What is his final velocity?
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When Momentum changes, we know that object’s motion changes. We define a change in motion
as an __A____________________. According to Newton’s 2nd Law, this means that there must
then be a _N_________ __F________________. We also know, from our study of kinematics, that
we can define acceleration as a change in velocity divided by the time it takes for the velocity to
change. This is important; we define a change in momentum as mass times change in velocity.
From the definition of acceleration, we can say that our change in velocity is equal to Acceleration
times Time. From this, we can then say that our change in Momentum is equal to Mass times
Acceleration times Time; we know that Mass times Acceleration is equal to Net Force.
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What this all means, then, is that we can state the following relationship (which is how Isaac Newton
actually stated his definition of Net Force):
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In the equation above, we define the product of ΣF * t as an __I__________________, which is
symbolized with the letter _____. [Don’t confuse this with the unit of Energy, the Joule.] The above
equation is then referred to as the “__I__________________
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__M_________________
__T_______________.”
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Impulse is a __V_____________ quantity; the direction of the impulse is the same as the direction of
the Net Force. The unit for Impulse is the same as Momentum: kg*m/s. [Note: another acceptable
unit is N*s].
Ex. 6: A 10 kg mass, initially at rest, is subjected to a net force of 20 N for a time of 4 seconds. What is
the impulse delivered to the mass? What is the change in its momentum? What is its final speed?