A 5.00-kg object is attached to one end of a horizontal spring that has a negligible mass and a spring constant of 420 N/m. The other end of the spring is fixed to a wall. The spring is compressed by 10.0 cm from its equilibrium position and released from rest.

Question: What is the speed of the object when it is 8.00 cm from equilibrium?

3 answers

PE stored in spring: 1/2 k x^2 or
1/2 * 420* .1^2 joules

PE stored in spring at 8 cm:
1/2 * 420*.08^2

so the Kinetic energy in the object is equal to the energy released..

1/2 m v^2=PE at 10cm -PE at 8cm
solve for velocity v

you are incorrect

I am wrong. you are correct