Two balls of clay known masses hang from the ceiling on masslessstrings of equal

Question

Two balls of clay known masses hang from the ceiling on masslessstrings of equal length. They barely touch when both hang atrest. One ball is pulled back until its string is45o, the released. It swings down, collides withthe second ball, and they stick together. To determine theangle to which the balls wing to the opposite side, you need toinvoke: A. Conservation of momentum B. Conservation of mechanicalenergy C. Both conservation of momentum andconservation of mechanical energy D. Either, but not both. E. These principles alone are not sufficientto find the angle Two balls of clay known masses hang from the ceiling on masslessstrings of equal length. They barely touch when both hang atrest. One ball is pulled back until its string is45o, the released. It swings down, collides withthe second ball, and they stick together. To determine theangle to which the balls wing to the opposite side, you need toinvoke: A. Conservation of momentum B. Conservation of mechanicalenergy C. Both conservation of momentum andconservation of mechanical energy D. Either, but not both. E. These principles alone are not sufficientto find the angle

Explanation / Answer

The answer is C. Both conservation ofmomentum and conservation of mechanical energy You need: 1.Conservation of energy to calculate the velocity of the firstball of clay by the time it descends: mgh=1/2mu2 [calculate h by using h=L(1-cos45)] 2.Conservation of momentum to find out the final velocity of theballs of clay using: m1u1+m2u2=(m1+m2)v ---note:u2=0 3.Conservation of energy to calculate the max height the balls ofclay will go by using: 1/2(m1+m2)v2=mgh Once you have h, h=L(1-cos), solve for Thus the answer is C

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