Transcript Slide 1

Chapter 6.1
Review
1. What is
needed to cause
a change in
momentum?
An unbalanced
force is needed to
cause a change in
momentum.
2. The speed of a car is
tripled. By how much is
the momentum
changed? By how
much is the kinetic
energy changed?
The momentum is
tripled, mv.
The kinetic energy is
multiplied by a factor
2
of nine, ½ mv .
3. A ball is moving up with
a speed of 8 m/s. A few
seconds later, it is falling
at 8 m/s. Is the momentum
of the ball the same at
these two points? Is the
kinetic energy the same?
The momentum is NOT the
same. Momentum is a vector
and the ball is going in two
different directions.
However, the kinetic energy
IS the same, kinetic energy is
NOT a vector.
4. A dog with a mass
of 55 kg is running
north with a velocity
of 15 m/s. What is his
momentum?
p = mv
p = 55 kg x 15 m/s
p = 825 kgm/s
5. Toonces, a 22 kg cat is
driving an 1180 kg car at a
velocity of 25 m/s east.
What is the total
momentum of the
Toonces and the car?
p = mv
p = (22 + 1180 kg) x 25 m/s
p = 30050 kgm/s east
6. What is
Toonces’
momentum in
problem 5?
p = mv
p = (22 kg) x 25 m/s
p = 550 kgm/s east
7. What is
the car’s
momentum in
problem 5?
p = mv
p = (1180 kg) x 25 m/s
p = 29500 kgm/s east
8. A 12 kg bird is flying
15 m/s to the north. A few
moments later, the bird is
flying 15 m/s to the south.
Is the change in the bird’s
momentum zero? If not,
what is the change in the
bird’s momentum?
NO. The change in velocity is
not zero. Since the bird is
moving in the opposite
direction, the velocity change
is 15 + 15 m/s.
p = mv
p = 12 kg x 30 m/s
p = 360 kgm/s south
9. Josh Hamilton hits a
38 m/s pitch. The 0.15 kg
baseball leaves his bat in
the opposite direction at
41 m/s. What is the
change in momentum of
the baseball?
p = mv
p = 0.15 kg x (38 + 41 m/s)
p = 0.15 kg x (79 m/s)
p = 11.85 kgm/s
10. How are
impulse and
momentum
related?
Impulse is equal
to the change in
momentum.
Ft = Dmv
11. A 0.4 kg football is
kicked off a tee. It leaves
the foot of the kicker at
21 m/s. What impulse was
delivered to the football by
the kicker’s foot?
Impulse is equal to
change in
momentum.
Impulse = Dmv
Impulse = 0.4 x 21
Impulse = 8.4 Ns
12. An arrow of mass
0.023 kg is moving
35 m/s. If a target slows
the arrow to a stop in
0.34 seconds, what force
did the target apply to the
arrow?
Ft = Dmv
F x 0.34 s =
0.023 kg x 35 m/s
F x 0.34 = 0.805
F = 2.37 N
13. Bengie Molina catches
a 0.15 kg baseball pitched
at 40 m/s. If he slows
the ball to a stop in
0.15 seconds, what force
did he apply?
Ft = Dmv
F x 0.15 s =
0.15 kg x 40 m/s
F x 0.15 = 6
F = 40 N
14. A 50 kg ice skater
throws a 15 kg box
east at 10 m/s. What
is the velocity of the
skater?
Dmv = Dmv
50 x v = 15 x 10
50v = 150
v = 3 m/s
15. A soccer ball with a mass of
0.48 kg is moving at 20 m/s. If
the ball collides with a player’s
head (mass = 5 kg) and the ball
rebounds in the opposite
direction at 20 m/s, what is the
velocity of the player’s head?
mv + mv = mv + mv
0.48 x 20 + 5 x 0 =
0.48 x -20 + 5 x v
9.2 = -9.2 + 5v
18.4 = 5v
v = 3.68 m/s
16. A bullet is fired at
1000 m/s to the west.
The mass of the bullet is
5 grams. What is the
recoil momentum of the
gun?
p 0 = pf
p = mv
p = 0.005 x 1000
p = 5 kgm/s
17. If the gun in
question 16 has a
mass of 1.1 kg,
what is the gun’s
recoil velocity?
p = mv
5 kgm/s = 1.1v
v = 4.55 m/s
18. A 40 kg roller skater
pushes a 60 kg roller skater.
If the 60 kg skater rolls away
at a velocity of 5 m/s north,
what is the velocity of the
40 kg skater?
Dmv = Dmv
40 x v = 60 x 5
40v = 300
v = 7.5 m/s