One of the efficient concepts that can help us find the number of turns of the cable is through the concept of induced voltage or electromotive force given by Faraday's law. The electromotive force or emf can be described as,

Where,
N = Number of loops
B = Magnetic Field
A = Cross-sectional Area
= Angular velocity
Re-arrange to find N,

Our values are given as,




Replacing at our equation we have:



Therefore the number of loops of wire should be wound on the square armature is 32 loops
Answer:
175.96 g
Explanation:
Potential energy required for the man to climb 7.07 km = m g h.
= 64 x 9.8 x 7070
= 4.434 x 10⁶ J
= 4.434 X 10⁶ / 4.2 cals
= 1.0557 x 10⁶ cals
= 1.0557 x 10⁶ / 6000 g of butter
= 175.96 g of butter.
Answer:
At night we experience quietness more. At this time, sounds of object will be heard more clearer
To develop this problem it is necessary to apply the concepts related to Wavelength, The relationship between speed, voltage and linear density as well as frequency. By definition the speed as a function of the tension and the linear density is given by

Where,
T = Tension
Linear density
Our data are given by
Tension , T = 70 N
Linear density , 
Amplitude , A = 7 cm = 0.07 m
Period , t = 0.35 s
Replacing our values,



Speed can also be expressed as

Re-arrange to find \lambda

Where,
f = Frequency,
Which is also described in function of the Period as,



Therefore replacing to find 


Therefore the wavelength of the waves created in the string is 3.49m
If you could please give me a already given speed I could estimate it. since there is no speed shown you wouldn't be able to estimate the speed of the moving train.