A block of mass m moving with a velocity `v_(0)` on a smooth horizontal surface strikes and compresses a spring ofstiffuess k till mass coines to rest as shown in the figure. This phenomenon is observed by two observers :
(a) Standing on the horizontal surface
(b) standing on the block

To an observer B, when the block is compressing the spring :

Options

A. velocity of the block is decreasing
B. retardation of the block is increasing
C. kinetic energy of the block is zero
D. all of the above

Answer

C