Suppose that you are standing on a train accelerating at 0.39g. What minimum coefficient of static friction must exist between y
our feet and the floor if you are not to slide? Static friction is the friction that exist between a stationary object and the surface on which it is resting. Coefficient of friction tells us how strongly the two surfaces grip each other. Static friction and coefficient of friction are related to each other by the relation;
Fs=μsN
where,
Fs=Force of static friction
μs=Coefficient of friction
N=Normal force
Because you know that gravity is in m/s^2 so, period will be measured in seconds. You know the cable is 12m long and gravity is 9.81 solve for T (period) 2π12sqrt(9.81)=6.94922