The formula to calculate the kinetic energy (K) of a particle executing SHM is given by
K=21k(A2−y2)...(1)
Substitute the values of the known parameters into equation (1) and solve to calculate the value of the unknown parameter.
K==⇒=⇒⇒⇒21×k×(A2−A2cos230∘)21×k×A2sin230∘200=21×1.0×10x×(0.4)2×(21)21002×10x102=10x−2x−2=2x=4