# Homework Help: This guy is stealing my bases

1. Oct 9, 2011

### KendrickLamar

This guy is stealing my bases!!!

nvm delete this please i got it

Last edited: Oct 9, 2011
2. Oct 9, 2011

### WJSwanson

Re: This guy is stealing my bases!!!

I got the same ballpark (get it?) answer, -661J, using both common methods:

$W = \int^{x_{f}}_{x_{i}} F_{k} . ds = F_{k} . s = -Fs$

where F (the force vector) is given by $\frac{m\Delta v}{\Delta t}$ where Δt is given by $\Delta t = \frac{2\Delta x}{\Delta v}$

as well as

$W_{k} = \Delta K = -\frac{m(\Delta v)^{2}}{2}$

so I would say you can most likely enter -664J assuming you minded your p's and q's properly with your significant figures. (The smallest number of significant figures I saw was actually 2, in the 68kg, so that might be an issue.)

But the work done by friction is by convention usually negative: the force of friction categorically acts in the opposite direction of the displacement, so the dot product of the friction-force function and the differential displacement will always be negative. (Because $\theta = \pi$.)