Physics Help Forum work done to lift a body

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 Sep 19th 2008, 03:30 AM #1 Member     Join Date: Apr 2008 Posts: 31 work done to lift a body $\displaystyle W=\frac{1}{2}F_R\cdot{R}$ Am I approaching the problem correctly? Thanks.
Sep 20th 2008, 04:16 PM   #2

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 Originally Posted by disclaimer $\displaystyle W=\frac{1}{2}F_R\cdot{R}$ Am I approaching the problem correctly? Thanks.
The equation for the line forming the top of the boundary is
$\displaystyle F = \frac{F_R}{R} \cdot r$
and the work done is
$\displaystyle W = \int_0^RF~dr$
(The applied force F and dr are in the same direction.)

So we have
$\displaystyle W = \int_0^R \frac{F_Rr}{R}~dr$

$\displaystyle W = \frac{F_R}{2R} \cdot R^2 + 0$

$\displaystyle W = \frac{1}{2}F_R R$

(Or you could simply find the area of the triangle, as I suspect you did.)

-Dan
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