# Physics

A radioactive substance decays from 2.0kg to 1.6kg in 156 days.
What is the decay constant and the half life of the substance?

1. If T is the half life in days
(1.6)/2.0 = (T/156)^(1/2)
0.8 = 0.08006 T^1/2
9.992 = T^1/2
T = 99.8 days

The decay constant k is related to the half life by

k = ln2/T

posted by drwls
2. A weight of 40 N is suspended from a spring that has a constant of 200 N/m the system is subjected to a harmonic driving force of frequency 10.5 hz resulting in a forced- motion amplitude of 3 cm determine the max value of the driving force

posted by Mina

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