More inelastic problems Homework Question - How Far Do They Slide?

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In summary, the conversation discusses a physics problem involving a stuntman and a villain on a window ledge. The goal is to calculate how far the two individuals will slide after colliding, given their masses and the coefficient of kinetic friction on the floor. The proposed solution method involves finding the potential energy of the stuntman and subtracting the friction caused by the two bodies to determine the remaining energy in the system. However, it is noted that this approach is incorrect as the collision is inelastic and energy is not conserved. Instead, the initial joint speed must be calculated before applying conservation of energy to solve the problem.
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Spraypaint
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Homework Statement



A movie stuntman (mass 81.8 kg) stands on a window ledge 7.33 m above the floor. Grabbing a rope attached to a chandelier, he swings down to grapple with the movie’s villain (mass 66.4 kg), who is standing directly under the chandelier. (Assume that the stuntman’s center of mass moves downward 7.33 m. He releases the rope just as he reaches the villain) If the coefficient of kinetic friction of their bodies with the floor is uk = 0.71, how far do they slide?

Homework Equations





The Attempt at a Solution


So what I did is first solve for the potential of the stuntman ( 81.8 * 9.8 * 7.33). Then subtract out the friction caused by the two people ( total mass * 9.8 * .71). This is the energy left to the system. So set this equal to F * d where force is equal to total mass * 9.8. And that's how I get my d, which is wrong.
 
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  • #2
Spraypaint said:
So what I did is first solve for the potential of the stuntman ( 81.8 * 9.8 * 7.33). Then subtract out the friction caused by the two people ( total mass * 9.8 * .71). This is the energy left to the system. So set this equal to F * d where force is equal to total mass * 9.8. And that's how I get my d, which is wrong.

Hi Spraypaint! :smile:

The collision is inelastic … energy is not conserved in the collision

you have to find the initial joint speed before you can start to apply conservation of energy. :wink:
 
  • #3



I would like to point out that the approach taken in this solution is incorrect. The problem involves a collision between two bodies, so it cannot be solved using energy conservation alone. Instead, the conservation of linear momentum should be used to determine the distance the two bodies will slide after the collision. The initial momentum of the stuntman and the villain before the collision is equal to the final momentum after the collision. This can be expressed as m1v1 + m2v2 = (m1 + m2)v, where m1 and m2 are the masses of the stuntman and the villain, respectively, v1 and v2 are their initial velocities, and v is their final velocity after the collision. From this equation, the final velocity can be calculated, and then the distance they will slide can be determined using the equation v^2 = u^2 + 2as, where u is the initial velocity (which is zero in this case), a is the coefficient of kinetic friction, and s is the distance. It is important to note that the mass of the rope and the chandelier should also be taken into account in the calculation of the total mass.
 

1. What is an inelastic problem?

An inelastic problem is a type of problem or situation where the solution or outcome is not easily changed or influenced by external factors. This means that the solution is not flexible and cannot be easily altered or adapted to different circumstances.

2. How are inelastic problems different from elastic problems?

Elastic problems are those where the solution can be easily modified or changed by external factors. This means that the solution is flexible and can adapt to different circumstances. In contrast, inelastic problems have a fixed solution that is not easily changed.

3. What are some examples of inelastic problems?

Examples of inelastic problems include climate change, poverty, and addiction. These problems have solutions that are difficult to change or influence, and often require long-term and complex interventions.

4. How do scientists approach inelastic problems?

Scientists approach inelastic problems by using evidence-based methods and strategies. This involves conducting research, analyzing data, and collaborating with other experts to develop effective solutions that can address these complex problems.

5. Can inelastic problems ever be solved?

Inelastic problems may not have a single, definitive solution, but they can be managed and improved over time. Scientists work towards finding ways to mitigate and reduce the impact of these problems, but they may never have a complete and final solution.

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