Kinetic energy is the energy that is associated with motion. It is the energy possessed by an object that is moving. It is calculated from one-half the product of the mass and the square of the velocity of the object. From this, we can calculate the mass of the object. We do as follows:
KE = mv^2/2
500 J = m(5 m/s)^2 / 2
m = 40 kg
I think it is "A'' 'It moves along straight lines in air and changes direction when it enters water.
Answer:

Explanation:
We first identify the elements of this simple harmonic motion:
The amplitude A is 8.8cm, because it's the maximum distance the mass can go away from the equilibrium point. In meters, it is equivalent to 0.088m.
The angular frequency ω can be calculated with the formula:

Where k is the spring constant and m is the mass of the particle.
Now, since the spring starts stretched at its maximum, the appropriate function to use is the positive cosine in the equation of simple harmonic motion:

Finally, the equation of the motion of the system is:
or

Friction is causing the skateboard to stop rolling.