One end of a horizontal spring with force constant 76.0 N/mN/m is attached to a vertical post. A 4.00-kgkg can of beans is attached to the other end. The spring is initially neither stretched nor compressed. A constant horizontal force of 53.0 NN is then applied to the can, in the direction away from the post.

a. What is the speed of the block when the spring is stretched 0.400 m?
b. At that instant, what are the magnitude and direction of the acceleration of the block?