MHR • Advanced Functions 12 Solutions 660

f) 40 = 94.54(0.978) t
log 40
94.54 = log(0.978)t
log 40 = t log 0.978
94.54
log 40
t =
94.54
log 0.978
t &= 38.7
30 = 94.54(0.978) t
log 30
94.54 = log(0.978)t
log 30 = t log 0.978
94.54
log 30
t =
94.54
log 0.978
t &= 51.6
0 = 94.54(0.978) t
0
log
94.54 = log(0.978)t
0
log = t log 0.978
94.54
0
log
t =
94.54
log 0.978
t!is!undefined
This makes sense because the water cannot cool less than room temperature.
Chapter 7 Section 5 Question 10 Page 406
"
a) 150 !120 = 10log I %
2
$ '
# &
I 1
"
30 = 10log I %
2
$ '
# &
I 1
"
3 = log I %
2
$ '
# &
10 3 = I 2
I 1
I 1
1000 = I 2
I 1
The ratio of the intensities is 1000. Rocco’s signal needs to be boosted to match Biff’s sound
level.
1
b) 1000 ÷ = 1000 !10 000
10 000
= 10 000 000
= 10 7
The sound crew should reduce the drums by a factor of 10 7 .
Chapter 7 Section 5 Question 11 Page 406
Solutions to Achievement Check questions are provided in the Teacher’s Resource.
MHR • Advanced Functions 12 Solutions 727