4 different worksheets. Since they are separate complete them as separate tasks
Name:
Date:
PRACTICE
112m
4 sec
Impulse
3.1
READ
СРО
A change in momentum for an object is equal to impulse. Momentum changes when velocity changes.
impulse = change in momentum
Force is what changes velocity. Therefore, when momentum changes a force must be involved for a period of
time. The following equation relates impulse to change in momentum.
Force x time = Final momentum – Initial momentum
Fxt = mv2 – MV
Momentum (p) is expressed in units of kg-m/s; m is the mass of the object, in kg; and v is the velocity of the
object in m/sec. Impulse is expressed in units of N sec.
1 N sec = 1 kg: m/sec because 1 newton = 1 kg-m/sec?:
1 N-sec = 1
kg-m
x sec = 1
1 kg-m
Sec?
sec
EXAMPLES
t
1 =
A net force of 50 newtons is applied to a 20-kilogram cart that is already moving at 1 meter per second. The final
speed of the cart was 3 meters per second. For how long was the force applied?
Looking for
Solution
The speed of the cart after 3 seconds.
mv2-mvi
F
Given
Force applied = 50 newtons
(20 kg)(3 m/sec) – (20 kg)(1 m/sec)
50 N
Mass of the car = 20 kilograms
(60 kg-m/sec)-(20 kg-m/sec)
Initial speed of the cart = 1 m/sec
50 N
Final speed of the cart = 3 m/sec
(40 kg-m/sec)
Relationships
= 0.8 sec
50 N
time = change in momentum – Force
The force was applied to the cart for 0.8 second.
mv2-mv,
F
t =
1 =
Page 2 of 3
PRACTICE
112m
4 sec
3.1
PRACTICE
1. A net force of 100 newtons is applied to a 20-kilogram cart that is already moving at 3 meter per second. The
final speed of the cart was 8 meters per second. For how long was the force applied?
Looking for
Solution
Given
Relationships
2.
a.
A 3-kilogram ball is accelerated from rest to a speed of 10 m/sec.
What is the ball’s change in momentum?
b. What is the impulse?
c. If a constant force of 40 newtons is applied to change the momentum in this situation, for how long does
the force act?
a.
c.
a.
3. A 2,000-kilogram car uses a braking force of 12,000 newtons to stop in 5 seconds.
What impulse acts on the car?
b. What is the change in momentum of the car?
What is the initial speed of the car?
4. A 60-kilogram high jumper lands on a mat after her jump. The mat brings her to a stop after 1 second. She
was traveling at 5.0 m/sec when she landed on the mat. Note: The speed of the jumper at the top of her jump,
before she started to fall toward the mat, was 0 m/sec.
What is the change in momentum for the jumper?
b. What is the force felt by the jumper upon impact with the mat?
5. A 0.5-kilogram soccer ball is kicked with a force of 50 newtons for 0.2 seconds. The ball was at rest before
the kick. What is the speed of the soccer ball after the kick?
A baseball player hits a 0.155-kilogram fastball traveling at 44.0 m/sec into center field at a speed of 50.0
m/sec. If the impact lasts for 0.00450 second, with what force does he hit the baseball?
7. Tow Sawyer launches his 180-kilogram raft on the Mississippi River by pushing on it with a force of
75 newtons. How long must Tom push on the raft to accelerate it to a speed of 2.0 m/sec?
8. In terms of impulse, why is the ride much more comfortable when an airplane is flying at constant speed
versus when it is taking off or landing?
Thought questions
6.
9. In certain martial arts, people practice breaking a piece of wood with the side of their bare hand. Use your
understanding of impulse to explain how this can be done without injury to the hand.
10. If identical bullets are shot from a pistol and a rifle, a bullet shot from the rifle will travel at a higher speed
than a bullet from the pistol. Why? (Hints: Assume shooting force is the same in each case. The barrel of the
rifle is longer than the barrel of the pistol.)
Page 3 of 3
PRACTICE
112m
4 sec
3.1
11. Boxers attempt to move with an opponent’s punch when it is thrown. In other words, a boxer moves in
the same direction as their opponent’s punch. This movement may prevent a knockout blow being
delivered by their opponent. Explain how.
12. Show that the relationship between impulse and the change in momentum is another way of stating Newton’s
second law of motion.
13. Mats in a gym, airbags, and padding in sports uniforms are used to protect people from being injured.
Explain why these soft objects used instead of rigid objects using your understanding of impulse and change
of momentum
Page 2 of 2
PRACTICE
112m
4 sec
3.1
PRACTICE z
1. If a ball is rolling at a velocity of 1.5 m/sec and has a momentum of 10.0 kg-m/sec, what is the mass of the
ball?
a.
2. What is the velocity of an object that has a mass of 2.5 kilogram and a momentum of 1,000 kg m/sec?
3. Tiger Woods hits 45.0-gram golf ball, giving it a speed of 75.0 m/sec. What momentum has Tiger given to
the golf ball?
4. A 400-kilogram cannon fires a 10-kilogram cannonball at 20 m/sec. If the cannon is on wheels, at what
velocity does it move backward? (This backward motion is called recoil velocity.)
5. “Big” Al stands on a skateboard at rest and throws a 0.5-kilogram rock at a velocity of 10.0 m/sec. “Big” Al
moves back at 0.05 m/sec. What is the combined mass of “Big” Al and the skateboard?
6. As the boat in which he is riding approaches a dock at 3.0 m/sec, Jasper stands up in the boat and jumps
toward the dock. Jasper applies an average force of 800 newtons on the boat for 0.30 seconds as he jumps.
How much momentum does Jasper’s 80-kilogram body have as it lands on the dock?
b. What is Jasper’s speed on the dock?
7. Daryl the delivery guy gets out of his pizza delivery truck forgetting to set the parking brake. The
2,000 kilogram truck rolls down hill reaching a speed of 30 m/sec just before hitting a large oak tree. The
vehicle stops 0.72 seconds after first making contact with the tree.
How much momentum does the truck have just before hitting the tree?
What is the average force applied by the tree?
8. Two billion people jump up in the air at the same time with an average velocity of 7.0 m/sec. If the mass of
an average person is 60 kilograms and the mass of Earth is 5.98 x 1024 kilograms:
What is the total momentum of the two billion people?
b. What is the effect of their action on Earth?
9. Tammy, a lifeguard, spots a swimmer struggling in the surf and jumps from her lifeguard chair to the sand
beach. She makes contact with the sand at a speed of 6.00 m/sec leaving an indentation in the sand
0.10 meters deep.
If Tammy’s mass is 60. kilograms, what is momentum as she first touches the sand?
b. What is the average force applied on Tammy by the sand beach?
10. When a gun is fired, the shooter describes the sensation of the gun kicking. Explain this in terms of
momentum conservation.
a.
b.
a.
a.
11. What does it mean to say that momentum is conserved?
PRACTICE
Use your knowledge about solving equations to work out the following problems:
1.
If the truck has a mass of 2,000 kilograms, what is its momentum? Express your answer in kg.m/sec.
2.
3.
If the car has a mass of 1,000 kilograms, what is its momentum?
An 8-kilogram bowling ball is rolling in a straight line toward you. If its momentum is 16 kg.m/sec, how fast
is it traveling?
4.
A beach ball is rolling in a straight line toward you at a speed of 0.5 m/sec. Its momentum is 0.25 kg-m/sec.
What is the mass of the beach ball?
5. A 4,000-kilogram truck travels in a straight line at 10.0 m/sec. What is its momentum?
6. A 1,400-kilogram car is also traveling in a straight line. Its momentum is equal to that of the truck in the
previous question. What is the velocity of the car?
7. Which would take more force to stop in 10 seconds: an 8.0-kilogram ball rolling in a straight line at a speed
of 0.2 m/sec or a 4.0-kilogram ball rolling along the same path at a speed of 1.0 m/sec?
8.
The momentum of a car traveling in a straight line at 20 m/sec is 24,500 kg-m/sec. What is the car’s mass?
9. A 0.14-kilogram baseball is thrown in a straight line at a velocity of 30 m/sec. What is the momentum of the
baseball?
10. Another pitcher throws the same baseball in a straight line. Its momentum is 2.1 kg-m/sec. What is the
velocity of the ball?
11. A 1-kilogram turtle crawls in a straight line at a speed of 0.01 m/sec. What is the turtle’s momentum?
Name
Period
Date
“Understanding Car Crashes
It’s Basics Physics”
Video Discussion Questions
Student
Post-Video
Questions
Directions:
After viewing the video, answer the following questions in the space
provided. Be prepared to discuss your responses with your classmates
while in small groups or as an entire class.
Post-Video “Crash” Questions
1. Ever tried to stop a 150 pound (68 kg) cannonball fired towards you
at 30 mph (48 km/hr.)? No, probably not. But you may have tried to
brace yourself in a car collision. How are the two situations similar?
2 Show mathematically why an 80,000 pound (36,000 kg) big rig
traveling 2 mph (0.89 m/s) has the SAME MOMENTUM as a 4,000
pound (1,800 kg) sport utility vehicle traveling 40 mph (18 m/s).
3. During the Egg-Throwing Demonstration, which egg experienced the
greater impulse, the egg that hit the wall or the bed sheet? (Be careful
here! Which egg experienced the greater force of impact? Which egg
experienced the greater time of impact?
“CRASH COURSE” ACTIVITY
“Understanding Car Crashes
It’s Basics Physics”
Video Discussion Questions
Student
Post-Video
Questions
4. Explain how the fortunate race car drivers survived their high speed
crashes.
a. Describe other examples where momentum is reduced by applying
a smaller collision force over a longer impact time (or where things
“give way” during a collision to lessen the impact force)?
6. Which would be more damaging to your car: having a head-on collision
with an identical car traveling at an identical speed or driving head on
into the Vehicle Research Center’s 320,000 pound (145,455 kg) deformable
concrete crash barrier? Explain.
Name
Period
Date
TUM
TER
Student
Post-Video
Questions
“Understanding Car Crashes
It’s Basics Physics”
Video Discussion Questions
SER
7. Show mathematically why a small increase in your vehicle’s speed
results in a tremendous increase in your vehicle’s kinetic energy. (For
example: doubling your speed from 30 mph to 60 mph results in a
quadrupling of your kinetic energy.)
8. The Law of Conservation of Energy states: energy cannot be created
or destroyed; it can be transformed from one form to another but the
total amount of energy never changes. Car crashes can involve huge
amounts of energy. How does the crashworthiness of the car affect
the transfer and transformations of the energy and, ultimately,
protect the occupants?
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