How long would it take

1. Jun 22, 2012

Justhelp

How long would it take....

1. The problem statement, all variables and given/known data
This is a problem that followed a bunch of others so I will post what I got for those as well.

Here is the problem: How long would it take Kirk to fall to the valley floor?

5.29s or 3.47s or 11.836s or 2.43s or none of those. I am not getting any of them, I don't know if I am doing it correct. I am using the d=1/2gt^2 formula and get 3.645s. Distance being 35.721m and g being 9.8.

And that number is not any of the choices listed.... is it non of the above?

2. Relevant equations

Captain James T Kirk is on vacation in Ca. He is climbing 59m above the floor of the valley when he stops to rest. Cpt. Kirk has a mass of 110kg. What is the potential energy of Kirk? I got 63602J, using the PE=mgh formula.
His kinetic energy would be 0 when he rests.

Kirk suddenly looses his grip and begins to fall! How far does he fall in 2.7s? I got 35.721m using d=1/2gt^2

What is Kirks velocity after falling for 2.7s? I got 13.23m/s using the v=d/t formula.

What is his kinetic energy after falling for 2.7s? I am not sure about that one, but I got 9626.8095J using the kinetic formula KE=1/2mv^2

What is his potential energy after falling 2.7s? Using the potential energy formula P subscript E =mgh I came up with 38507.238J.

2. Jun 22, 2012

Justhelp

Re: How long would it take....

I should also say that the number I got for what his kinetic energy after falling for 2.7s is not listed either. I just do not have anyone to compare my work with currently.

3. Jun 22, 2012

SammyS

Staff Emeritus
Re: How long would it take....

How far does he fall if he falls all the way to the valley floor.

BTW: (The correct answer is) there.)

4. Jun 22, 2012

Justhelp

Re: How long would it take....

Using d=rt?

5. Jun 22, 2012

Justhelp

Re: How long would it take....

But..I don't have time.

6. Jun 22, 2012

Justhelp

Re: How long would it take....

I can't use distance or time because the numbers I got were for 2.7s.

7. Jun 22, 2012

Staff: Mentor

Re: How long would it take....

His velocity after falling 2.7 sec is not d/t, because his velocity has been changing as he accelerates downward. d/t is his average velocity after 2.7 sec, not his instantaneous velocity. You know his acceleration and his initial velocity (zero), so, again, what is his velocity after 2.7 sec?

8. Jun 22, 2012

SammyS

Staff Emeritus
Re: How long would it take....

How far does he fall if he falls all the way to the valley floor?