Conservation of energy and work

In summary, the conversation discusses a scenario where a 70.4 kg man falls from a window and lands on a sidewalk, with a given height and cushion. The first question is solved for the man's speed before impact, which is 5.11 m/s. The second question asks for the average force exerted on the man if his fall is cushioned by only 0.508 cm. This can be solved using the equation F=ma, with the acceleration (a) being determined by using the equation Vf^2=Vi^2+2a(xf-xi), with Vf=5.11 m/s, Vi=0 m/s, xf=0, and xi=0.508 cm
  • #1
Knfoster
45
0

Homework Statement



A 70.4 kg man steps out of a window and falls (from rest) 1.33 m to a sidewalk. at is his speed just before his feet stke the pavement?

If the man falls with his knees and ankles locked, the only cushin for his fall is a 0.508 cm give in the pads of his feet. Calculate the erage force exerted on him bye ground in this situation. The avera force is sufficient to cause cartilage dage in the joints or to break bones.

Homework Equations



PE+KE=PE+KE (before and after)
W=F(xf-xi)cos theta
W=delta KE
PE=mgh
F=ma
KE=.5mv^2


The Attempt at a Solution



I already solved the first question and got 5.11 m/s.
I don't know how to set up the second problem to find the force.
Please help.
Thank you.
 
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  • #2
I think they want you to calculate the force (acceleration) that will be required if the deceleration is over the space of just 1/2 cm (.508 cm).
 
  • #3
ok. So F=ma, and I need to find acceleration to finish the problem. So Do I use Vf^2=Vi^2+2a(xf-xi) ? If so do I use 5.11 m/s for Vf and 0 m/s for Vo? Is xf=0 and xi=.508 cm?
 
  • #4
Knfoster said:
ok. So F=ma, and I need to find acceleration to finish the problem. So Do I use Vf^2=Vi^2+2a(xf-xi) ? If so do I use 5.11 m/s for Vf and 0 m/s for Vo? Is xf=0 and xi=.508 cm?

Looks to me like what they are asking.
 

1. What is the principle of conservation of energy?

The principle of conservation of energy states that energy cannot be created or destroyed, but can only be transformed from one form to another. This means that the total amount of energy in a closed system remains constant.

2. How does work relate to the conservation of energy?

Work is defined as the transfer of energy from one object to another by applying a force. According to the principle of conservation of energy, the total amount of energy in a system must remain constant, so any work done on an object will result in a transfer of energy to that object.

3. What are some examples of conservation of energy in everyday life?

Some examples of conservation of energy in everyday life include turning off lights when not in use to conserve electrical energy, using public transportation or carpooling to reduce the use of fossil fuels, and using renewable energy sources like solar or wind power instead of non-renewable sources.

4. How is conservation of energy applied in scientific experiments?

In scientific experiments, conservation of energy is often used to check the validity of results. The total energy before and after an experiment should be the same, as energy cannot be created or destroyed. This helps to ensure that all energy transfers and transformations have been accounted for and that the results are accurate.

5. What are the implications of not following the principle of conservation of energy?

If the principle of conservation of energy is not followed, it could lead to a variety of consequences. For example, if energy is not properly conserved in a closed system, it could result in inaccurate scientific experiments or unsustainable use of resources. On a larger scale, not conserving energy can contribute to global issues such as climate change and depletion of natural resources.

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