Transcript AP Physics ID

AP Physics I.D
Impulse and Momentum
7.1 Impulse-Momentum Theorem
Momentum
• Product of mass and velocity
• It’s a vector Victor
Impulse (a vector and has same
direction as average force)
Examples of impulse
Ex. A golf ball with a mass of 0.050 kg is hit from a tee. The
velocity of the ball off the tee is 44 m/s. What is the a) impulse
for the ball and b) the average force if the time the club is in
contact with the ball is 9.1 EE – 4 s?
Ex. In a crash test, a 1.50 EE 3 kg car collides with a wall with
a speed of 15.0 m/s. The car bounces back from the wall with a
speed of 2.60 m/s. The car is in contact with the wall for 0.150
s. Find the average force exerted on the car by the wall.
p. 206: 3-5, 9, 12-14
4. 4.24 kg·m/s
12. 320 kg·m/s at 16º N of E
14. 344 N (find v and use impulse formula)
7.2 Conservation of Linear
Momentum
Two billiard balls on a Physicstown
(frictionless) table
Two types of forces on the
system
• Internal – forces that objects within the
system exert on each other
• External – forces that objects outside the
system exert on each other
A derivation from Newton’s Third
Law
Linear momentum is conserved
if the sum of the external forces
is zero (the momentum before
the collision is equal to the
momentum after the collision)
Ex. A Ford Excursion at rest with a mass of 1.80 EE 3 kg is
struck in the rear by a Ford Pinto with a mass of 9.0 EE 2 kg.
The cars become entangled and move in the initial direction of
the Pinto. What is the final velocity of the entangled cars if the
initial velocity of the Pinto is 20.0 m/s?
Rifle Recoil: Find the recoil velocity of a 5.0 kg rifle that shoots
a 0.050 kg bullet at a speed of 120 m/s.
p. 207: 15-16, 18, 20, 24; Rev. p.
123: 40, 43
16. 7.1 EE 5 m/s
18. 96 kg
20. 1.5 m
24. 2.2
40. a) 550 N
b) 7.2 m/s
7.3 Collisions in One Dimension
Elastic collision – momentum and
kinetic energy are conserved
(objects bounce off one another –
in real life this only happens at the
atomic level)
Inelastic collision – momentum is
conserved, but kinetic energy is
not
Completely inelastic collision –
all kinetic energy converted to
other forms of energy – the
objects stick together (thud)
Note: momentum is conserved if no
external forces act on the system, but
kinetic energy is conserved only in
elastic collisions.
Ex. A bullet with a mass of 0.0100 kg strikes, and is
embedded in a block (mass of 2.50 kg) that is suspended by a
thin cord. The block rises a vertical height of 0.650 m because
of the collision. What is the initial velocity of the bullet
assuming the collision is elastic?
7.4 Collision in Two Dimensions
If no external forces act on a system,
horizontal and vertical components of
momentum are conserved.
Ex. A ball moving with a speed of 3.0 m/s along the positive xaxis strikes a second ball with twice the mass initially at rest.
The first ball glances off the second and moves off at angle
above the x-axis while the second moves at an angle of 35º
below the x-axis at 1.0 m/s. Find the angle and speed of the
first ball after the collision.
84B2, 85B1, 01B2
84B2 – not hard. You
complete
85B1
a) 1.5 m/s
b) 667/1
c) 0.11 m
01B2
a) 0.42 m/s
b) Use the usual
kinematics (0.21 m)
c) 0.30 m/s
d) 0.015 kg·m/s