Question

One end of an ideal spring (spring constant k) is attached to a rigid wall and other end to a block kept on a horizontal smooth surface.The spring is always horizontal .The block is released from rest when the spring is elongated by x

(A) The maximum work done by the spring on the block in the subsequent motion is 1/2kx²  

(B) The block is at rest when the spring is in its undeformed state 

(C) The spring always does positive work when the block moves away from the wall. 

(D) The spring does negative work whenever the block slows down.

Answer 1

Correct option (A) (D)

Explanation:

Maximum work done by the spring = maximum loss in P.E. of the spring = 1/2kx²

The block will have maximum KE when the spring is in its undeformed state i.e., P.E =0 state 

When spring does negative work the kinetic energy of the block will decrease. 

While moving away from the wall the P E of the spring first decreases and then increases and therefore the K.E of the block first increases and then decreases.