Download Example +x direction 3 kg particle 1 kg particle Before explosion

Example
vi=0
Before explosion
1 m/s
??? m/s
After explosion
3 kg particle
1 kg particle
1
+x direction
Find the velocity of 1 kg object after explosion.
Surface has no friction.
(a)
(b)
(c)
(d)
(e)
1 m/s
2 m/s
3 m/s
4 m/s
None of above
Example 1: The archer
An archer stands at rest on
frictionless ice and fires a 0.50 kg
arrow horizontally at 50.0 m/s. The
combined mass of the archer and bow
is 60.0 kg. With what velocity does
the archer move across the ice after
firing the arrow?
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Elastic vs. Inelastic Collisions
In a collision within a system of particles
After
collision
Before
collision
Net kinetic energy:K
net
If
K net ,i  K net , f
If
K net ,i  K net , f
If
K net ,i  K net , f
 K1  K 2  ... 
1
1
m1v12  m2v22  ...
2
2
 elastic collision.
 inelastic collision.
and objects move together after collision
 perfectly inelastic collision.
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Elastic Collisions in 1-Dimension
Both total momentum & total kinetic energy are conserved.
m1v1,i  m2 v2,i  m1v1, f  m2 v2, f
v1i
&
1
1
1
1
m1v12i  m2 v22i  m1v12f  m2 v22 f
2
2
2
2
v2i
Before collision
m1
m2
v1f=?
v2f=?
+x direction
After collision
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In 1D elastic collision, if m1=m2, vi1=+10 m/s, v2i=0,
then, after collision v1f= _____ and v2f= _____.
V2i=0
V1i=10m/s
Before collision
m1
m2
v1f=?
After collision
v2f=?
+x direction
Collisions in Two Dimensions
If net external force is zero,

Or


Pnet ,i  Pnet , f
, where
net momentum is conserved.



Pnet  m1v1  m2 v2  ...
y
Pnet ,i , x  Pnet , f , x
V1
Pnet ,i , y  Pnet , f , y
If net kinetic energy is
conserved  Elastic collision
not conserved  Inelastic collision
If moving together after collision
 Perfectly Inelastic collision
(Kinetic energy is not conserved.)
v1
m1
v2 m2
x
V2
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Example 2: Collision at an intersection
A 1500 kg car traveling east with a
speed of 25 m/s collides at an
intersection with a 2500 kg van
traveling north at a speed of 20 m/s.
Find the direction and magnitude of
the velocity of the wreckage right
after the collision, assuming the
vehicles stick together after the
collision.
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