Physics Internet Activity: THE IMPULSE-MOMENTUM CHANGE THEOREM
Go to www.physicsclassroom.com and select > Physics Tutorial > Momentum and its Conservation > Go
through “Lesson 1”.
Momentum
1) How would you define momentum?
mass in motion or inertia in motion
2) Momentum depends on what two factors?
mass and velocity
3) Write the equation for momentum. What is the symbol for momentum? What is the unit of measure
for momentum?
p = mv
p=momentum
(kg∙m/s)
4) What is the relationship between momentum and mass? What will happen to the momentum of an
object if you quadruple its mass without changing its motion?
directly proportional relationship; the momentum will quadruple if the
mass quadruples
5) What is the relationship between momentum and velocity? What will happen to the momentum of an
object if you double its velocity without changing its mass?
directly proportional relationship; momentum will double if velocity
doubles
6) Is momentum a vector or a scalar quantity?
vector quantity
7) A cart with a mass of 40. kg is moving west at 2.5 m/s. (Show your calculations)
a. What is its momentum?
p=mv = (40 kg)(2.5 m/s) = 100 kg∙m/s, west
b. What would be its momentum if it had twice the mass?
p=mv=(80 kg) (2.5 m/s) = 200 kg∙m/s, west
8) A bowling ball with a mass of 3.5 kg was rolling at a speed of 1.5 m/s. (Show your calculations)
a. What is the ball’s momentum?
p=mv=(3.5 kg)(1.5m/s)=5.3 kg∙m/s
b. If a force was added to the ball to reduce its velocity by half, what would be the new
momentum of the ball?
p=mv=(3.5kg)(0.75m/s)=2.7 kg∙m/s
9) There are three students running across the football field. All three students have the same momentum.
(Show your calculations)
a. Gary has a mass of 60. kg and a speed of 4.0 m/s. What would be his momentum?
p= mv=(60.kg)(4.0m/s)=240 kg∙m/s
b. Jenna has a mass of 55 kg. What would be her speed?
v=p/m=(240 kg∙m/s)/(55kg)=4.4m/s
c. Rick is running at 2.0 m/s. What would be his mass?
m=p/v=(240 kg∙m/s)/2.0m/s)=120kg
10) Which would have a greater momentum, a flying mosquito or a parked tractor trailer? Explain.
mosquito because it has mass and velocity while the tractor trailer has zero
velocity therefore zero momentum
11) Is it possible for a 60 kg cheetah to have a greater momentum than a 2300 kg elephant? Explain.
Yes, if the elephant’s velocity is much less than the cheetah, or the elephant
is not moving at all.
Momentum and Impulse Connection
12) To stop an object with momentum, it is necessary to apply a force against its motion for a given
period of time.
13) How would you apply force to slow down an object? How would you apply force to speed up an
object?
To slow down, apply force in the opposite direction of motion;
To speed up, apply force in the same direction of the motion
14) Using Newton’s 2nd law of motion, relate the acceleration of an object and its net force.
Acceleration and net force are directly proportional
15) Write an equation that shows that the impulse of an object is equal to its change in momentum.
Ft = m∆v
16) In a collision an object experiences a force
for a specific amount of time that results in a
change in momentum.
17) If a tennis racket is moving east to apply an impulse of 120 N∙s on a tennis ball that is moving west,
what would be the change in momentum of the tennis ball? 120 kg∙m/s
18)
Use the diagram below to answer questions a-d. Remember
that ∆v = vf - vi
7u
a. Why does case B have a greater change in velocity?
it changes from +30m/s to -28m/s ; change in velocity = -58 m/s
b. Why does case B have a greater acceleration?
because B has a greater change in velocity
c. Why does case B have a greater momentum change?
momentum depends on velocity, and case B has a greater velocity
d. Why does case B have a greater impulse?
impulse = change in momentum
19) Using the equations below, solve the following problems. Show your calculations.
Impulse = F∙t
∆p = m ∙ ∆v
p=mv
impulse = ∆p
Ft=m∆v
a. What is the impulse on an object receiving a force of 50. N in 2.5 s?
I=Ft = (50.N)(2.5s) = 130N∙s
b. What would be the change in momentum of an object if a force of 25 N is applied for 0.75 s on
the object?
I = Ft = (25N)(.75s)=19N∙s=change in momentum = 19 kg∙m/s
c. A 15 kg object is moving at 10. m/s north. How much impulse is needed to stop this object?
What direction is the impulse applied? If the impulse requires 3.2 s to stop the object, how
much force is required?
p=mv=(15kg)(10,m/s)=150 kg∙m/s = I = -150 N∙s
F=I/t = (-150N∙s)/(3.2s) = -47N
d. A force of 200. N leftward is applied to a 25 kg object for 12 s to accelerate it to a certain
velocity. What would be the change in momentum of this object? What would be its change in
velocity?
I=Ft=(200.N)(12s)=2400 N∙s = p=2400 kg∙m/s
v=p/m=(2400 kg∙m/s)/(25kg)=96m/s
Real-World Applications
20) What is the impulse-momentum change theorem?
Ft = m∆v
21) How does the time of collision affect the force of the collision?
When you increase the time of collision, you decrease the force of collision.
They are inversely proportional.
22) How do airbags help us during car collisions?
The airbag increases the time of collision resulting in the decrease of the
force of collision.
23) When you are jumping, how does bending your knees help during landing?
When you bend your knees, you increase the time of impact which decreases
the force of impact on your joints.
24) What is “rebounding”?
Rebounding is when colliding objects bounce off each other.
25) What is the difference in the change of velocity between a car that rebounds to that of a car that just
crumples upon impact? Which is more beneficial to the passengers during a car accident?
The change in velocity is greater when a car rebounds compared to it
crumpling upon impact.
It is more beneficial for the car to crumple because of less change in velocity
which means less change in momentum, which means less impulse on the
car.