fisica1-youn-e-freedman-exercicios-resolvidos

3
7.83: a) Along this line, x = y , so F
r
⋅ dl
r
= −αy
dy , and
y2
α 4 4
∫ Fydy
= − ( y2
− y1
) = −50.6
J.
y1
4
b) Along the first leg, dy = 0 and so F
r ⋅ d l
r
= 0 . Along the second leg, x = 3.00 m ,
so
F y
−( y
2
= 7.50 N m 2 ) , and
∫
y2
y1
2 3
F dy = −(7.5
3 N m )( y − y
y
2
3
1
) = −67.5
J.
c) The work done depends on the path, and the force is not conservative.
7.84: a)
b) (1): x = 0 along this leg, so F r = 0 and W = 0 . (2): Along this leg, y = 1.50 m , so
F
r ⋅ d l
r
2
= (3.00 N m)xdx
, and W = (1.50 N m)((1.50 m) − 0) = 3.38 J (3) F
r ⋅ d l
r
= 0 , so
W = 0 (4) y = 0 , so F r = 0 and W = 0 . The work done in moving around the closed path
is 3.38 J. c) The work done in moving around a closed path is not zero, and the force is
not conservative.