Answer:
Collisions
Follow Newton’s Third Law which tells us that
the force exerted by body A on body B in a
collision is equal and opposite to the force
exerted on body B by body A.
During a collision, external forces are ignored.
The time frame of the collision is very short.
The forces are impulsive forces (high force, short
duration).
Collision Types
Elastic: P is conserved, K is conserved
Inelastic: P is conserved, K is NOT conserved
Perfectly Inelastic means the bodies stick together
Problem: Collisions (1993)
10. Which of the following is true when an object of
mass m moving on a horizontal frictionless surface
hits and sticks to an object of mass M > m, which is
initially at rest on the surface?
(A) The collision is elastic.
(B) All of the initial kinetic energy of the less-massive
object is lost.
(C) The momentum of the objects that are stuck together
has a smaller magnitude than the initial momentum of
the less-massive object.
(D) The speed of the objects that are stuck together
will be less than the initial speed of the less-massive
object.
(E) The direction of motion of the objects that are stuck
together depends on whether the hit is a head-on
collision.
Explain your reasoning:
Ans. Again, by conservation of momentum, if the
mass increases, the velocity must decrease. pin = pout
Problem: Collisions (1993)
11. Two objects having the same mass travel
toward each other on a flat surface, each with a
speed of 10 meter per second relative to the
surface. The objects collide head-on and are
reported to rebound after the collision, each
with a speed of 20 meters per second relative
to the surface. Which of the following
assessments of this report is most accurate?
(A) Momentum was not conserved, therefore the report is false.
(B) If potential energy was released to the objects
during the collision, the report could be true.
(C) If the objects had different masses, the report could be true.
(D) If the surface was inclined, the report could be true.
(E) If there was no friction between the objects and the
surface, the report could be true.
Explain your reasoning:
Ans. Momentum is conserved provided that an
external force not be applied. If the objects have
potential energy stored, this could provide the force.
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