Hockey Puck Speed Measuring
A physics question for a friend?
A hockey puck (mass A = 0.10kg) moves along the ice in the x-direction at a speed of 8.0 m/s. It strikes a second puck (mass B = 0.40kg) which is initial at rest. After the collision, it is observed that puck A moves off at an angle of theta above the x-axis while puck B moves at an angle phi below the x-axis.
A). Write the equations that represent conservation of momentum (2 components: x- and y) for this event. Write the equation for conservation of energy.
B). If the final angles are measured to have the values theta = 60.0 degrees and phi = 30.0 degrees, determine whether this collision was elastic or inelastic. If you decide that the collision was inelastic, what amount of the initial kinetic energy is converted to another form as a result?
She’s still having trouble with this one. Can someone help please? 
A) * Momentum conservation:
x : mA.v0 = mA.vA.cos(theta) + mB.vB.cos(phi) (1)
y: mA.vA.sin(theta) = mB.vB.sin(phi) (2)
* Energy conservation:
1/2 mA.v0^2 = 1/2 mA.vA^2 + 1/2 mB.vB^2 + Q (3)
with Q – energy converted to other form
B) It surely inelastic.
(2) => vB = mA.vA.sin(theta)/[mB.sin(phi)] =[sqrt(3)/4] vA
(1) => v0 = vA.cos(theta) +(mB/mA)vB.cos(phi)
=> v0 =(1/2 + 3/2) vA = 2. vA
=> vA = v0/2 = 4.0 m/s, vB = sqrt(3) m/s
(3) => Q = 0.5×0.1×8^2 – 0.5×0.1×4^2 – 0.5×0.4×3 = 1.8 J
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