Download Class work February 6

College Physics
Class Work February 6, 2015
Mrs. Ashley
Name ______________________________________________
Conservation of Momentum: Total energy of an isolated system remains constant;
Rate of change in momentum of an object is equal to the net force applied to it.
Momentum change accounts for change in masses in a system
ΣF = Δp/Δt
ΣF = mv2 - mv1
Δt
What are ms?
Go over homework
1. What is the correct formula for finding the net force applied to an object that includes momentum?
ΣF = Δp/Δt
2. A 0.16 baseball is pitched at 41.0 m/s and is hit on a horizontal line drive straight back toward the
pitcher at 54.0 m/s. If the contact time between bat and ball is 3.00 X 10-3 calculate the average force
between the ball and bat during contact.
Conservation of Momentum: Total energy of an isolated system remains constant;
momentum before = momentum after
p = momentum vector
m = mass
v = velocity vector
p=mv
Useful when looking at collisions. There are elastic collisions and inelastic collisions.
2. A 9300 kg boxcar traveling at 15.0 m/s strikes a second boxcar at rest. The two stick together and
move off with a speed of 5.5 m/s. What is the mass of the second car?
Impulse is equal to the force X time.
F Δt = impulse
This is useful when looking at forces that act during a short time interval.
4. A 15 kg hammer strikes a nail at a velocity of 9.2 m/s and comes to rest in a time interval of 8.0 ms.
What is the impulse given to the nail? What is the average force acting on the nail?
Conservation of Energy and Momentum in Collisions
If the total energy just before a collision and just after a collision is the same, the total kinetic energy
is conserved and it is called an elastic collisions.
Total kinetic energy before = total Kinetic energy after
1/2 mava2 + 1/2 mbvb 2 = 1/2 mav'a2 + 1/2 mbv'b 2
If the kinetic energy is not conserve, these are inelastic collisions. Then the energy that is lost is
changed into other forms of energy. If two objects stick together as a result of a collision the
collisions is said to be completely inelastic.
KEa + KEb = KE'a + KE'b + Thermal Energy and other forms of energy
Head on Elastic Collisions:
va - vb = -( va - vb)