Answer:
Part a)

Part b)
t = 12 s
Explanation:
Part a)
Tension in the rope at a distance x from the lower end is given as

so the speed of the wave at that position is given as

here we know that

now we have


Part b)
time taken by the wave to reach the top is given as




Answer:
Explanation:
Given
charge of first body 
charge of second body 
Particle 1 is at origin and particle 2 is at 
third Particle which charge +q must be placed left of
because it will repel the q charge while
will attract it
suppose it is placed at a distance of x m








Answer: Option (b) is the correct answer.
Explanation:
The given data is as follows.
F =
N
g = 9.8 m/s
radius =
=
= 15 cm = 0.15 m (as 1 m = 100 cm)
Formula to calculate depth is as follows.
F = 
or, h =
h =
= 751 m
Thus, we can conclude that the maximum depth in a lake to which the submarine can go without damaging the window is closest 750 m.
B
Assume north and east as two sides of a right angled triangle. magnitude of the distance is then given by the length of the hypotenuse which is 
where a = 1.2 km north
and b = 1.6 km east
magnitude = 2 km
Direction is given by the angle between them, that is atan(a/b) = 36.86 deg north of east = 53.1 deg east of north.
I hope my answer helped u under stand better