The spring has a stiffness k=200n/m and is unstretched when the 25 kg block is at a. determine the acceleration of the block when s=0.4m. the contact surface between the block and the plane has

To solve this we are going to use the formula fro the force applied to a spring: 
where
is the spring constant 
is the extension 

Since we know the , we can replace that in our formula and solve for  :


where
is the acceleration 
is the spring constant
is the extension 
is the mass

We know for our problem that , , and . So lets replace those values in our formula to find :




We can conclude that the acceleration of the block when s=0.4m is .

Heptagon is the correct ans