A spring has a spring constant of 75N/m. The spring is compressed 15cm and a 2kg

Question

A spring has a spring constant of 75N/m. The spring is compressed 15cm and a 2kg ball is attached to the spring in its compressed state.

a. When the spring is released, what is the kinetic energy of the ball as it leaves the spring?

b. What is the potential energy of the spring in its compressed state?

c. What is the potential energy of the spring as the ball leaves the spring?

d. What is the total energy of the system (ball and spring) when the spring is compressed?

e. What is the total energy of the system (ball and spring) when the ball leaves the spring?

I know, its a lot of questions but I have no idea how to work on it. I have a few equations, but I have no idea how to apply them. :
U=mgy (potential difference = mass*gravity*y displacement)
K=.5mv^2 (Kinetic energy=.5*mass*velocity^2)

Explanation / Answer

The spring constant k = 75N/m the compression of the spring x = 15cm = 15*10^-2m the mass of the ball m = 2kg (a) From law of conservation of energy
the kinetic energy of the ball is K = 1/2 kx^2
   = 0.5 (75)(15*10^-2m)^2
   =   0.84 J
(b) The potential energy of the spring in its compressed state    U = 1/2 kx^2 = 0.84J (c) The potential energy of the spring as the ball leaves    U = 0 (d) The total energy of the system is E = K+U = 0 + U = 0.84J (e) When the spring released, the total energy is    E = K+U = 0.84 + 0 = 0.84J Here the energy is conserved so it is constant at every point of the system.
  

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