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Momentum and Elastic Collisions 
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#1
Nov509, 06:57 PM

P: 13

1. The problem statement, all variables and given/known data
In a pool game, the cue ball, which has an initial speed of 8.0 m/s, make an elastic collision with the eight ball, which is initially at rest. After the collision, the eight ball moves at an angle of 30° to the original direction of the cue ball. 2. Relevant equations V8 = Velocity of 8ball Vc = Velocity of cue ball (1)Epx = m*V8*cos(30) + m*Vc*cos(x) = m*8 (2)Epy = m*V8*sin(30) + m*Vc*sin(x) = 0 (3).5*m*Vi^2 = .5*m*V8^2 + .5*m*Vc^2 3. The attempt at a solution While these equations are technically solvable, they are nearly impossible by hand. Solving (3) for one velocity and using substitution twice I get: sin(x)^2 cos(30)*cos(x) + sin(30)*cos(30)*cos(x)  sin(30)*cos(x)^2 = 1/8 Is there an easier way to solve this since I know I will not be able to solve this equation myself? 


#2
Nov509, 07:48 PM

HW Helper
P: 4,433

(1)Epx = m*V8*cos(30) + m*Vc*cos(x) = m*8
(2)Epy = m*V8*sin(30) + m*Vc*sin(x) = 0 Rewrite these two equations as m*V8*cos(30) = m*8  m*Vc*cos(x) (1) m*V8*sin(30) =  m*Vc*sin(x) (2) Square both sides of eq.1 and 2 and add them. After simplification you will get the value of vc*cos(x) From the conservation of energy equation, find the value of vc. Then you can find the angle x. 


#3
Nov509, 07:56 PM

P: 13

Awesome, thanks so much!



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