Download Elastic and Inelastic Collisions and more Study notes Physics in PDF only on Docsity!
D
Elastic and Inelastic Collisions
In an ELASTIC collision, energy is conserved (KEbefore = KEafter or Ki = Kf).
In an INELASTIC collision, energy is NOT conserved. (Ki > Kf).
Example: A 1 kg block which is sliding at 10 m/s across a frictionless surface suddenly collides with a stationary 2 kg block. They stick together and they move towards an inclined plane of angle 37 o. How far up the incline will they move? Was the collision elastic or inelastic?
Example: A 10 kg pendulum bob is hanging at rest at the end of a 4 meter long rope. A 500 gram ball is thrown horizontally at the pendulum bob with a speed of 5.0000 m/s. It strikes the pendulum bob, and them bounces straight backward at a speed of 4.5238 m/s. What angle will the pendulum bob swing through? Was the collision elastic or inelastic?
For ELASTIC, HEAD-ON, 1D Collisions
Conservation of Momentum:
m 1 v 1 i m 2 v 2 i m 1 v 1 f m 2 v 2 f
If we know all but one velocity (or mass), we can find the missing velocity (or mass) .
Conservation of Energy:
1 2
m 1 v 1 i 2
1 2
m 2 v 2 i 2
1 2
m 1 v 1 f 2
1 2
m 2 v 2 f 2
Put the two equations together (carefully and with many steps ) and you get the following equations.
v 1 f
m 1 m 2 m 1 m 2
v 1 i ^
2 m 2 m 1 m 2
v 2 i
v 2 f
2 m 1 m 1 m 2
v 1 i ^
m 1 m 2 m 1 m 2
v 2 i
With these equations, we can find BOTH velocities of the balls after the collision by just
using the initial velocity of the balls and the masses of the balls!
Special Case: If v2i = 0, then what happens when …..
a) m 1 (^) m 2 ___________________________________________________
b) m 1 (^) m 2 ___________________________________________________
c) m 1 (^) m 2 ___________________________________________________
d) m 1 (^) m 2 ___________________________________________________
e) m 1 (^) m 2 ___________________________________________________
BEFORE
v 1 i v 1 f
m 1 m 2 m 1 m 2
v2i
v2f
AFTER
