- #1
myxomatosii
- 80
- 0
Homework Statement
The graph shows the net external force component F cos θ along the displacement as a function of the magnitude of the displacement s. The graph applies to a 65 kg ice skater.
http://img9.imageshack.us/img9/3441/0671.gif (a) How much work does the net force component do on the skater from 0 to 3.0 m?
93 Joules (Correct)
(b) How much work does the net force component do on the skater from 3.0 m to 6.0 m?
0 Joules (Correct)
(c) If the initial speed of the skater is 2.4 m/s when s = 0, what is the speed when s = 6.0 m?
Homework Equations
W=F(Δx)
KE=.5mv2
The Attempt at a Solution
For part C.
Here is my attempt.
Firstly, I do not understand the reason that FCosΘ was used as a Force instead of simply F, due to the way the graph is drawn, I chose to simply represent it as F, which may have been my mistake, but I doubt that.
I know the WorkTotal done on the skater was 93 Joules. So I thought that perhaps the change in Kinetic Energy would be equivalent to 93 Joules, allowing me to solve for Vf.
So I tried that below.
FCosΘ=31N
W=FCosΘ(Δx)
FCosΘ(Δx)=.5mvf2-.5mvi2
.5mvf2=FCosΘ(Δx)+5mvi2
vf2=(2(FCosΘ(Δx))/m) + vi2
which means to solve for vf I would use.
vf=((2(FCosΘ(Δx))/m)0.5)+vi
Yet that answer is wrong. I think my concept of this problem is wrong..
For Δx I used 3 instead of 6, since the force drops off to zero and the environment is frictionless, so it shouldn't make a difference.
Last edited by a moderator: