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Impulse and Momentum
Terminology
 Impulse: FΔt, or the product of the average force on
object and the time interval over which it acts
(measures in Newton-seconds)
 Momentum: mv, or the product of the object’s mass
and the objects velocity
 Impulse-momentum Theorem: FΔt= pf –pi ; The
impulse on an object is equal to the object’s final
momentum mines the object’s initial momentum (p=
momentum)
Concepts
 The momentum of an object is the product of its
mass and velocity and is a vector quantitiy.
 The impulse of an object is the average net force
exerts on the object multiplied by the time interval
over which the force acts.
 The impulse on an object is equal to the change in
momentum of the object.
Questions
 A pitcher claims he can throw a 0.151 kg baseball with as much
momentum as a 3.0 g bullet moving with a speed of 1.50 103 m/s.
Which of the following is true
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a) ball has greater kinetic energy.
b) both have the same kinetic energy.
c) the bullet has greater kinetic energy.
None of the above
 A pitcher throws a 0.15 kg baseball so that it crosses home
plate horizontally with a speed of 10 m/s. It is hit straight back
at the pitcher with a final speed of 24 m/s. Assume the
direction of the initial motion of the baseball to be positive.
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What is the impulse delivered to the ball?
Find the average force exerted by the bat on the ball if the two are in
contact for 2.0 10-3 s.
Equations
 F=MA
 F=M (ΔV/ ΔT)
 P=MV
 FΔt= MΔV
 P= momentum
 V=veolicity
 M= mass
 F= force
 T= time
Conservation of Linear
Momentum in Collisions
Terminology
 Closed system: a system that does not gain or lose
mass
 Isolated system: a closed system on which the net
external force is zero
 Law of conservation of momentum: states that the
momentum of any closed, isolated system does not
change
Concepts and Equations
 In a linear collision, momentum is neither
gained nor loss. Momentum is transferred to
another object.
 ½m1iv1i² + ½m2iv2i²= ½m1fv1f² + ½m2fv2f²
 m1v1i + m2v2i= m1v1f + m2v2f
 m1v1i + m2iv2i= vf (m1+ m2)
Quesions
 A 1245 kg car traveling initially with a speed of 25.0 m/s in an easterly direction
crashes into the rear end of a 9100 kg truck moving in the same direction at 20.0
m/s. The velocity of the car right after the collision is 18.0 m/s to the east.
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What is the velocity of the truck right after the collision?
 In a football game, a receiver is standing still, having just caught a pass.
Before he can move, a tackler, running at a velocity of +4.8 m/s, grabs
him. The tackler holds onto the receiver, and the two move off together
with a velocity of +2.6 m/s. The mass of the tackler is 116 kg. Assuming
that momentum is conserved, find the mass of the receiver.
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A) 121 kg
B)107 kg
C) 73 kg
D) 98 kg