Work and Energy Problem?
Question by ☮♥♫: Work and Energy Problem?
We’re working on work and energy right now, and I’m kind of confused. Here’s a problem we were assigned. I’m unsure on how to solve it. If you could help me out a bit (give me a hint or explain the steps), I would be so grateful! Thank you so much!
In 1936, Col. Harry Froboess of Switzerland jumped into the ocean from the airship Graf Hindenburg, which was 1.20 x 10² m above the water’s surface. Assiming Froboess had a mass of 72.0 kg, what was his kinetic energy at the moment he was 30.0 m from the water’s surface? What was his speed at that moment? Neglect the air resistance.
I know the formula for finding kinetic energy (KE = ½mv²) and potential energy (PE = mgh). But they don’t give you velocity, so I’m just kind of confused on how you would find the kinetic energy based on what they give you.
Any help would be great.
Thank you so much once again!
Best answer:
Answer by Kɥmǝr
Energy is conserved: E initial = E final
a) @ 30.0 m
mgh1 = mgh2 + 1/2mv^2
(72)(9.81)(1.20 x 10^2) – (72)(9.81)(30) = KE = 63 568.8 J
b) @ 30.0 m
KE = 1/2mv^2
v = sqrt((2KE)/m) = sqrt((2*63 568.8)/72)) = 42.02 m/s
Know better? Leave your own answer in the comments!
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about 3 months ago
We know that Energy inital is equal to Energy final:
Ei=Ef
We know that we have potential energy at the begining, but no kinetic energy. We also know that there is kinetic energy AND potential energy at the 30 meter point. So we could say:
PEi=KE + PEf
mgd1=1/2mv^2 + mgd2
So we begin to plug in numbers:
(72)(9.81)(120)=(1/2)(72)(Vf)^2 + (72)(9.81)(30)
84758.4=37Vf + 211.89.6
Then just use algerbra to solve from there:
63568.8=37Vf
1718.075=Vf
So we can conclude that the final velocity was 1718.08 m/s.
For finding kinetic energy, just plug in your new velocity in the formula.
Or instead of doing what I did, set your equation like this:
72)(9.81)(120)=KEf + (72)(9.81)(30)
Then find your final velocity.
I hope this helps.
about 3 months ago
PE+KE= total mechanical energy
total mechanical energy (or PE at max height)= 84672 J
PE 30m above sea level = 21168 J
21168 J + KE = 84672 J
KE=63504 J
and the speed at this height
KE=1/2mv^2
63504=1/2(72kg x v^2)
v=42 m/s