Momentum Extension
Name
—
Per
1. When considering weapons for defense against attacking zombies, the most important
consideration is stopping ability. If the motion of the undead can be reduced or stopped
there may be enough time for a survivor to escape.
Two survivors are discussing the merits of the weapons they have looted from the ruins of the
sporting goods store. Matt has a high-powered hunting rifle that fires a 0.05 kg bullet at 1000
rn/s He observes that his bullets often pass right through attacking zombies Kerry has a shotgun
that fires 0.1 kg of birdshot at 500 mIs. The small particles of ammunition from her weapon
penetrate a short distance into the flesh of the zombies but never go all the way through.
a) Matt insists that his high-powered weapon would be much better at stopping a zombie
shambling toward them. Use conservation of momentum to determine whether he is
correct. What assumptions did you make in your analysis?
Maff and his weapon
Kerry and her weapon
Choice of
ammo zombie
ammo, zombie
Initial state
Just before ammo strikes zombie
Just before ammo strikes zombie
Final state
After ammo strikes zombie
After amino strikes zombie
system objects
Sketchand
label initial
and frnal states
Calculate
initial
momentum of
ammo
Calculate final
momentum of
ammo. Make
reasonable
assumptions
about its
velocity.
Calculate
initial
momentum of
zombie. Make
reasonable
assumptions
about its mass
and velocity.
Momentum Extension
Name:
Per:
:.—‘
Which weapon
will be more
effective in
slowing the
zombie?
Explain.
b) Jimmy has a shotgun just like Kerry’s. He fmds himself cornered by a 90 kg zombie that
is shambling toward him at 2 mIs. He has four shells left in his repeating shotgun, and no
time to reload before he will be torn apart. Can he stop the zombie? Describe the
assumptions you made in your analysis.
4
j
F
0
-I
c) Josh has a 4 kg axe, which he can swing at 12 mIs. When he uses it on a zombie, it thunks
into moldering flesh and stops dead. Katelyn has a big 6 kg mallet which she can swing at
8 m/s. When she uses it on a zombie, it bounces off the zombie in the opposite direction
at almost the same speed. If they are facing identical zombies, shambling at the same
speed toward each of them, which has a better chance of stopping the zombie long
enough to escape? What assumptions did you make?
Momentum Extension
Name:
Per:
2. Jason Kidd, high in the air, drops a 0.60-kg basketball so that it reaches the floor falling
vertically at 6.0 mIs. The ball rebounds upward at a speed of 5.2 mIs, Determine the ball’s
change in momentum (magnitude and direction), Determine the average net force exerted
by the floor on the ball if the collision lasts 0.12 s.
3. The bone in the upper part of the cheek (the zygomatic bone) can be fractured by a 900-N
force lasting 6.0 ms or longer. A hockey puck can easily provide such a force when
hitting an unprotected face, (a) What change in velocity of a 0.11-kg hockey puck is
needed to provide that impulsive force? What assumptions did you make? (b) A padded
facemask doubles the stopping time. By how much does it change the force on the face?
Explain.
Momentum Extension
Name:
Per:
4. An 80-g arrow shot from a bow passes through an apple balanced on William Tell’s head.
The arrow has a speed of 50 m/s before hitting the apple; after passing through the apple,
the arrow is moving at 40 mIs. The apple has a mass of 100 g. Determine the fmal speed
of the apple.
5. A baseball bat stays in contact with a 0.145-kg baseball for 1.4 x i0 s. The average
force exerted by the bat on the ball is 9000 N If the ball has an initial velocity of 30 m/s
toward the bat and the force of the bat causes the ball’s motion to reverse direction, what
is the ball’s speed as it leaves the bat
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6. A tennis ball traveling horizontally at a speed of 45.0 mIs hits a wall and rebounds in the
opposite direction. The time interval for the collision is about 0.014 s and the mass of the
ball is 0.14 kg. Make a list of quantities you can determine using this information and
determine four of them. Assume that the ball rebounds at the same speed.