Answer:
We can think that the girl is initial over the skateboard, when she jumps forward, most of the force that she applies is downwards, so the force is transmitted from the skateboard to the ground.
Now, as she jumps forward, there is also some force applied in the horizontal direction, this force will affect the skateboard, accelerating it in the opposite direction (backward).
As the skateboard is way less heavy than the girl, the acceleration that the skateboard experiences will be bigger. Now, we can not estimate how much the skateboard moves, because we do not know the initial velocity of the skateboard.
B = 0.018 T Ans,
Since, it is moving in a circular path, thus, centripetal force will act on it i.e.
F =

where, m is the mass of the object, v is the velocity and r is the radius of circular path.
And, since a positive charge is moving, it will create magnetic force which is equal to F = qvB
where q is the charge, v is the velocity of the particle and B is the magnetic field.
Now, the two forces will be equal,
i.e.

= qvB
⇒

= qB
⇒B =

<span>putting the values, we get,
</span>
use q = 1.6 * 10^ -19
⇒ B = 0.018 T
To develop this problem we will use the concepts related to Speed in a string that is governed by Tension (T) and linear density (µ)

Our values are given as:

Replacing we have that the velocity is



From the theory of wave propagation the average power wave is given as

Where,
A = Amplitude
Angular velocity


Replacing,


Therefore the amplitude of the wave should be 0.0165m
C Weight is the gravitational pull on an object