A Spring with Spring Constant 800 N/m Compressed 0 $\mu$ _k = 0

A spring with spring constant 800 N/m compressed 0.200 m is released and projects a 0.800 kg mass along a frictionless surface.The mass reaches a surface area where $\mu$ _k = 0.400 and comes to a stop.The following student solution contains at least one error.What is the error? $$\frac { 1 } { 2 } \left( 800 \frac { \mathrm { N } } { \mathrm { m } } \right) ( 0.200 \mathrm {~m} ) ^ { 2 } = \frac { 1 } { 2 } ( 0.500 \mathrm {~kg} ) \left( 8.00 \frac { \mathrm { m } } { \mathrm { s } } \right) ^ { 2 } + 0.400 ( 0.500 \mathrm {~kg} ) \left( 9.80 \frac { \mathrm { m } } { \mathrm { s } ^ { 2 } } \right) ( 8.16 \mathrm {~m} )$$

A) The elastic potential energy is equal only to the kinetic energy on the right,and is never equal to the internal thermal energy.
B) The elastic potential energy is equal only to the internal thermal energy on the right,and is never equal to the kinetic energy.
C) The elastic potential energy is equal to either the kinetic energy or the internal thermal energy on the right,but not to their sum,depending on the part of the problem being done.
D) Elastic potential energy cannot end up as internal energy change caused by friction.
E) Change in mechanical energy by friction cannot end up as elastic potential energy.