Q.

A block of mass 2 kg is attached to one end of a massless spring whose other end is fixed at a wall. The spring-mass system moves on a frictionless horizontal table. The spring's natural length is 2 m and spring constant is 200 N/m. The block is pushed such that the length of the spring becomes 1 m and then released. At distance xm (x < 2) from the wall the speed of the block will be :          [2025]

1 10[10(2×x)3/2]m/s  
2 10[1(2x)2]1/2m/s  
3 [1(2x)2]m/s  
4 10[1(2x)2]m/s  

Ans.

(2)

Given, Natural length of spring = 2 m

Initial compression is spring (xi)=1m

Final compression in spring (xf)=(2x)m

Using energy conservation: Ki+Ui=Kf+Uf

0+12Kxi2=12mv2+12Kxf2

12mv2=12K(xi2xf2)

12×2×v2=12×200×(12(2x)2)

v2=100[1(2x)2]

 v=10[1(2x)2]1/2