What is the Mass Ratio m/M in an Inelastic Collision?

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SUMMARY

The discussion focuses on calculating the mass ratio m/M in an inelastic collision involving George of the Jungle and a gorilla. The scenario involves both characters swinging from vines and eventually colliding at the lowest point of their swings. Key equations utilized include angular momentum (L = mvr), potential energy (U = mvh), and kinetic energy (K = 1/2 mv²). The final equations derived lead to a straightforward calculation of the mass ratio using conservation of momentum and energy principles.

PREREQUISITES
  • Understanding of angular momentum and its formula (L = mvr).
  • Knowledge of potential energy and kinetic energy equations.
  • Familiarity with the concept of inelastic collisions in physics.
  • Ability to manipulate algebraic equations to solve for unknowns.
NEXT STEPS
  • Study the principles of conservation of momentum in inelastic collisions.
  • Learn more about energy conservation in mechanical systems.
  • Explore the effects of angles on potential and kinetic energy calculations.
  • Investigate real-world applications of angular momentum in collision scenarios.
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Students studying physics, particularly those focusing on mechanics and energy conservation, as well as educators looking for practical examples of inelastic collisions.

DkMuse
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Homework Statement


George of the Jungle, with mass m, swings on a light vine hanging from a
stationary branch. A second vine of equal length hangs from the same point,
and a gorilla of larger mass M swings in the oposite direction on it.
Both vines are horizontal when the primates start from rest at the same
moment. George and the ape meet at the lowest point in their swings.
Each is afraid that one vine will break, so they grab each other and hang on.
They swing upward together, reaching a point where the vines make an
angle of 35.0° with the vertical.
Find the value of the ratio m/M.

Homework Equations


Angular Momentum - L = mvr
Potential Energy - U = mvh
Kinetic Energy - K = 1/2 mv^2

The Attempt at a Solution


When both the man and ape start from rest the potential energy is
U = mgh, where h = r-rcosθ, r being the length of the vine
at 0°, cos 0° = 1, r-r =0
so U = mg

The knetic energy at the bottom given by K = 1/2 mv^2
setting an equality of K=U
1/2 mv^2 = mg
v= sqrt 2g
This would apply to both the man and the ape.
vM = vm = vf - right?

The potential energy of the man/ape system would be
U = (M+m) g r(1-cos 35°)

The kinetic energy of the man/ape system would be
1/2v^2(M-m)
So
1/2v^2(M-m) = (M+m) g r(1-cos 35°)
would be one equation for energy
and
Mvr + mvr = (M+m)vr
would equate angular momentum

... How do I continue to get a ratio of m/M?
 
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Would it be proper to say the man lost his kinetic energy after the
collision and write the final energy equation as:
1/2(M+m)vF^2 = (M+m)gh where h= r(1-cos35)
and vF = sqrt 2gr(1-cos35)

then vM would be sqrt 2g

Um = m(vm)gh, where h = (r-rcos180), cos 180 =-1, r-(-r) r+r = 2r
1/2m(vm)^2 = m(vm)g2r
vm would be sqrt 2g4r

Do I then plug the 3 velocities into the first momentum equation:
M vM + m vm = (M+m) vF

I still don't think enough will cancel out to me a ratio of m/M.
 
If I go back to my original assumption that both man and ape have the same initial
velocity and discount that one is at 0 degrees and the other is at 180 degrees
I can write their energy formulas as:
mgR = 1/2mv^2 and MgR = 1/2Mv^2
v = sqrt 2gR
Then if I write the momentum formula as:
(M-m)v = (M+m)v2
and write the collision energy formula as
1/2(M+m)v2^2 = (M+m) gR(1-cos35)
v2 = sqrt 2gR(1-cos35)
Sub back into the momentum formula with the two
velocities:
(M-m)sqrt 2gR = (M+m) sqrt 2gr (1-cos35)
From there it is pretty straightforward.
 

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