# Some energy questions

1. Apr 2, 2007

### harmeet_angel

1. The problem statement, all variables and given/known data
If a kayaker doubles her power output, and the resistive force due to the water remains same, by what factor does her speed changes(provided that her initial speed was constant, and is v0)?

2. Relevant equations
Power = Fd/t

3. The attempt at a solution

So, first I found the resistive force, using initial power (Pi) and initial speed (v0)
Pi=F(v0)
F=air resistance since the net force is0
Therefore I got the air resistance to be:
F=(Pi)/(v0)

And if she doubles her power, that means her applied force would be more than air resistance, and thus there would be net acceleration, and I can find new v using time or distance. But neither of them is given in the question.. so I couldn't find another way to solve this problem.

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and for the questions that attached along with this post, I am wondering about the second question(#68) it consists of two strings,
if it means that word needed it
0.5x^2(k2+k1)-mgx?
(work required to stretch the first string, and then the second string, and as gravity helps)
http://ca.geocities.com/cheemaharmeet/lastscan.jpg [Broken]
and for those two questions do i need to subtract by mgx?
cuz they say work required, so if that means we also have to exclude gravitational work?

Last edited by a moderator: May 2, 2017