42. The power consumed by the system is
P
=
1
20%
cm∆T
t
=
1
20%
(4.18 J/g
·
◦
C)(200
× 10
3
cm
3
)(1 g/cm
3
)(40
◦
C
− 20
◦
C)
(1.0 h)(3600 s/h)
=
2.3
× 10
4
W .
The area needed is then
A =
2.3
× 10
4
W
700 W/m
2
= 3 3 m
2
.
42. The power consumed by the system is
P
=
1
20%
cm∆T
t
=
1
20%
(4.18 J/g
·
◦
C)(200
× 10
3
cm
3
)(1 g/cm
3
)(40
◦
C
− 20
◦
C)
(1.0 h)(3600 s/h)
=
2.3
× 10
4
W .
The area needed is then
A =
2.3
× 10
4
W
700 W/m
2
= 3 3 m
2
.