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BradP
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Homework Statement
Two hard spheres collide elastically. Sphere 1 has a mass of 2 kg and an initial velocity of 3 m/s. Sphere 2 has a mass of 4 kg and is initially at rest. Sphere 1 collides head on with sphere 2 and comes to an immediate stop. Solve for the velocity of mass 2 using (a) conservation of momentum and (b) conservation of kinetic energy.
Homework Equations
Momentum = constant
m1*v1 = m2*v2
Kinetic energy = constant
m1*(v1^2) = m2*(v2)^2
The Attempt at a Solution
Using conservation of momentum,
2*3 = 4*v
v = 1.5 m/s.
Using conservation of kinetic energy,
.5*2*3^2=.5*4*v^2
v = 2.12 m/s.
My question is why the velocities are different. If this collision is elastic, shouldn't using kinetic energy and conservation of momentum give the same answer?