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

In summary, two primates, George and a gorilla, with masses m and M respectively, swing on two vines of equal length and meet at the lowest point. They grab onto each other and swing upwards, reaching an angle of 35.0° with the vertical. Using equations for angular momentum and energy, a ratio of m/M can be found by setting the kinetic energy of the system equal to the potential energy and solving for the velocities of each primate. By assuming they have the same initial velocity, the final equation simplifies to (M-m)sqrt 2gR = (M+m) sqrt 2gr (1-cos35), allowing the ratio to be calculated.
  • #1
DkMuse
3
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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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  • #2
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.
 
  • #3
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.
 

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

What is "Inelastic Collision Mass Ratio"?

"Inelastic Collision Mass Ratio" refers to the ratio of the masses of two objects involved in an inelastic collision. Inelastic collisions occur when two objects collide and stick together, resulting in a loss of kinetic energy.

How is the "Inelastic Collision Mass Ratio" calculated?

The "Inelastic Collision Mass Ratio" is calculated by dividing the mass of one object by the mass of the other object involved in the collision. This ratio can also be expressed as a decimal or percentage.

What is the significance of the "Inelastic Collision Mass Ratio"?

The "Inelastic Collision Mass Ratio" is significant because it can help determine the final velocity and momentum of the objects after the collision. It also helps in understanding the amount of kinetic energy that is lost during the collision.

How does the "Inelastic Collision Mass Ratio" affect the outcome of the collision?

The "Inelastic Collision Mass Ratio" directly affects the outcome of the collision. A higher mass ratio means that the lighter object will experience a greater change in velocity and momentum, while the heavier object will experience a smaller change. This results in a larger loss of kinetic energy and a more significant change in the objects' final velocities.

What are some real-life examples of "Inelastic Collision Mass Ratio"?

An example of "Inelastic Collision Mass Ratio" can be seen in a car crash. The ratio of the masses of the two cars involved in the collision will affect the severity of the crash and the resulting damage. Another example is a ball hitting a stationary object, such as a wall. The ratio of the mass of the ball to the mass of the wall will determine how much the ball will bounce back after the collision.

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