71. We take derivatives and let dg
≈ ∆g and dT ≈ ∆T . The derivative of Eq. 16-28 is
dT
dg
= 2π
1
2
−L/g
2
L/g
which (after dividing the left side by T and the right side by 2π
L/g) can be written
∆T
T
=
−
1
2
∆g
g
where both sides have also been multiplied by dg
→ ∆g. To make the units consistent, we write
∆T
T
=
2.5 min
1 day
=
2.5 min
1440 min
= 0.00174 .
Therefore, with g = 9.81 m/s
2
, we ob tain
0.00174 =
−
1
2
∆g
9.81 m/s
2
=
⇒ ∆g = −0.034 m/s
2
which yields g
= g + ∆g = 9.78 m/s
2
.