Download Momentum, Impulse and Law of Conservation of Momentum

Momentum, Impulse and Law
of Conservation of Momentum
Starter Questions
Starter 1
Momentum problems
1. What is the momentum of a 45 kg
boulder rolling at 3.5 m/s?
2. What is the mass of a boulder that is
rolling at 4.7 m/s and has a momentum
of 891 kg x m/s?
3. What is the speed of a 40.1 kg boulder
that has a momentum of 342 kg x m/s?
Starter #2—Use the impulse equation—solve on a
separate sheet of paper
1.
2.
3.
4.
5.
What is the impulse that changes the momentum of a boulder if a
force of 356 N is applied to the boulder for 4.5 s?
Solve problems 26-27 found on page 140.
How much force is applied to a cart if the application time of the
force is 12 seconds and the impulse is 245 N x s (or kg x m/s)
How long must a force of 65 N be applied to a cart if the impulse
is 455 N x s?
Suppose three objects received a force; the first object for 4.5 s,
the second object for 1.5 s and the third object for 3.1 s. The
impulse for each was 28.1 N x s. How much force was applied to
each object?
Starter 3
(reading from pg. 131) Figure 8.10
Momentum of cannon and cannonball
Read Page 131
• Read 1st paragraph
• What does Newton’s 3rd law have to say about the net
force of the cannon-cannonball system?
• Why is the momentum of the cannon-cannonball system
equal to zero before and after the firing?
Read Page 131
• Read 1st paragraph
• What does Newton’s 3rd law have to say about the net force of the
cannon-cannonball system?
• The net force of this system equals zero because the
action and reaction forces cancel each other out
• Why is the momentum of the cannon-cannonball system equal to
zero before and after the firing?
• The momentum in the system must be conserved; so if
the system starts with zero momentum, it must end
with zero momentum.
Read Page 131
• Read 2nd paragraph
• Why is momentum a vector quantity?
• Explain the difference between the momentum of the
cannon and the momentum of the cannonball, and the
momentum of the cannon-cannonball system.
Read Page 131
• Read 2nd paragraph
• Why is momentum a vector quantity?
• Momentum is a quantity that expresses both
magnitude and direction.
• Explain the difference between the momentum of the cannon and
the momentum of the cannonball, and the momentum of the
cannon-cannonball system.
• After the firing occurs, both the cannon and
cannonball have the same momentum (big mass, small
velocity vs. small mass, big velocity). But since the
momentum for each is moving in the opposite
direction, the momentums cancel out, causing the
cannon-cannonball system’s momentum to equal
zero.
Read Page 131
• Read 3rd paragraph
• Why do physicists use the word conserved for
momentum?
• State the law of conservation of momentum.
Read Page 131
• Read 3rd paragraph
• Why do physicists use the word conserved for
momentum?
• The word conserved refers to quantities
that do not change.
• State the law of conservation of momentum.
• In the absence of an external force, the
momentum of a system remains the same.
Read Page 131
• What does system mean?
• In terms of momentum conservation, why
does a cannon recoil when fired?
Final Thoughts about Page 131
• What does system mean?
• The word system refers to a group of interacting
elements that comprises a complex whole.
• In terms of momentum conservation, why
does a cannon recoil when fired?
• The cannon must recoil in order for
momentum to be conserved. (The
momentum of the cannon-cannonball system
was zero before the firing, and must remain
zero after the firing.)
Read Page 131
• What does conservation of momentum
mean?
• Conservation of momentum means that the amount
of momentum in a system does not change.
• Why is the momentum cannon-cannonball
system equal to zero?
• The momentum of the cannonball cancels
out the recoil of the cannon (both move in
opposite directions with an equal amount of
momentum.