Re: Anyone tell me what I'm doing wrong?

From: Tomasso (tom_at_r.so.com)
Date: 11/20/04 

Date: Sat, 20 Nov 2004 06:54:20 GMT

"Snis Pilbor" <snispilbor@yahoo.com> wrote in message news:d3a0a22a.0410301151.21de5750@posting.google.com...
> Hi,
>
> I have this problem, which I thought I solved, but the answer is wrong
> and I can't figure out why. I'll give the problem and my "solution":
>
> Problem: Julie starts skiing at the top of a 60 degree frictionless
> slope, at height 25m. At the bottom, a circular arc carries her
> through a 90 degree turn, and she then launches off a 3 meter high
> ramp. How far is her touchdown point from the base of the ramp?
>
> My strategy is to find her velocity when she makes the jump; then it's
> just a projectile problem with that initial velocity and 60 degree
> angle and initial height 3 meters. To find the velocity, I equate
> energy at the beginning, which is purely potential and in fact
> E=mgy=25mg, with energy at the jump, which is
> mgy+(1/2)mv^2=3mg+(1/2)mv^2. This yields v=sqrt(44g).
> I plug this into the projectile problem and (after solving the
> annoying quadratic, which I checked twice to make sure it wasn't just
> an arithmetic error) get a final distance of 39.765 meters (where I
> used g=9.81).
>
> The problem is... it's apparently wrong, and I can't figure out why.
> Any help will be greatly appreciated. Thanks in advance,
> Snis Pilbor

I get 42.738 m horizontal from take-off. NB, takeoff was 3m above ground level.

1.0589 s going up

1.3164 s going down

horizontal velocity is 17.9925 m/s

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