Answer:
2.67kg
Explanation:
The maximum velocity,
of a body experiencing simple harmonic motion is given by equation (1);

where
is the angular velocity and A is the amplitude.
The problem describes the oscillation of a loaded spring, and for a loaded spring the angular velocity is given by equation (2);

where k is the force constant of the spring and m is the loaded mass.
We can make
the subject of formula in equation (1) as follows;

We then combine equations (2) and (3) as follows;

According to the problem, the following are given;

We then substitute these values into equation (4) and solve for the unknown mass m as follows;


Squaring both sides, we obtain the following;

They are called magnets poles.
Use SUVAT where:
S = distance
U = initial velocity = 30m/s
V = end velocity = 0 m/s
A = acceleration = ?
T = time = 5 secs
then pick out the equation v = u + at
so:
0 = 30 + 5a
-30 / 5 = a
a = -6 m/s^2
Greater energy makes fast-moving water a greater force of erosion.