Average resistance force to stop an object

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SUMMARY

The discussion revolves around calculating the average resistance force exerted on a 50.0 kg diver who drops from a height of 10.0 m and comes to rest 5.0 m below the water's surface. The key equations used include gravitational potential energy (PEg = mgh) and kinetic energy (KE = 1/2 mv²). The average resistive force is determined to be -1500 N, as derived from the work-energy principle, where the work done equals the change in kinetic energy. The calculations reveal a discrepancy in the initial attempts, ultimately confirming that the average force is calculated using the work done over the distance the diver decelerates.

PREREQUISITES
  • Understanding of gravitational potential energy (PEg = mgh)
  • Knowledge of kinetic energy (KE = 1/2 mv²)
  • Familiarity with the work-energy principle
  • Basic algebra for solving equations
NEXT STEPS
  • Review the work-energy theorem and its applications in physics
  • Practice problems involving gravitational potential energy and kinetic energy
  • Explore the concept of average force and its calculation in different contexts
  • Investigate the effects of buoyancy and resistance forces in fluid dynamics
USEFUL FOR

Students studying physics, particularly those focusing on mechanics and energy concepts, as well as educators looking for examples of real-world applications of the work-energy principle.

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Homework Statement


A 50.0 kg diver steps off a 10.0 m high diving board and drops straight down into the water. If the diver comes to rest 5.0 m below the surface of the water, determine the average resistance force exerted on the diver by the water.


Homework Equations


PEg=mgh
KE=1/2 mv^2


The Attempt at a Solution


I did a similar question to this about a parachutist, but in that question there was a final velocity, in this one it seems like the final velocity would be 0? so I am lost...
 
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What is the diver's velocity as he hits the water?
What is his kinetic energy?
What is the change in kinetic energy when the diver decelerates from that velocity to 0?
What is the work done in decelerating the diver?
What is the average resistive force on the diver as he decelerates?
 
14.0m/s ?
4900J ?
wouldnt the change just be -4900J since the KEf would be 0?
so work done is the same as change in kinetic energy...
what am i doing wrong?
 
Work done is the change in kinetic energy, yes.

Work done is also the average force multiplied by distance across which it is applied...
 
so i divide the work done by 5.0m or 10.0m or 15.0m?
the back of the book says the answer should be -1500N and i can't get that no matter how i do it
 
I don't get that either. I get -1000N, taking g = 10 N/kg

KE= GPE = mgh = 5000J

All this is taken from the diver in the 5m of water: F = W/d = 5000/5 = 1000N.

But I'm quite drunk at the moment so I might be wrong.
 
haha alright well thanks for all the help.
 

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