Answer:
The period of the system of ladder and woman, T = 2.5 seconds
Explanation:
Mass of the ladder, 
Mass of the artiste, 
Length of the ladder, L = 42.0 kg
The total moment of inertia can be calculated using the equation:

D = L/2 = 3/2
D = 1.5 m
The frequency of the system of ladder and woman follows that of a physical pendulum which can be given by the equation:

The period of the system of ladder and woman is given by:
T = 1/f
T = 1/0.4
T = 2.5 seconds
Measuring mass with a balance
Number 3.
When you have two parallel wire and the charges are moving, they create a magnetic field around the wire (right-hand rule, thumb points in the direction of current).
If you want the math, here ya go:

F: magnetic force on the wire, L: length of the wire I: current in one wire I': current in other wire r: distance of the wire.
As we can see, two wires that has current through it will generate a force on each other.
Yes, eg., when 2 bodies move in opposite directions
, the relative velocity of each is greater than the individual velocity of either
Find the velocity of the object after one second.
v = vo + at
v = (0 m/s) + (9.8 m/s^2)(1 s)
v = 9.8 m/s
Now, using that, you can find the displacement in that one second between 1 and 2.
d = vot + (1/2)at^2
d = (9.8 m/s)(1 s) + (1/2)(9.8 m/s^2)(1 s)^2
d = 14.7 m