Q.

A massless spring gets elongated by amount x1 under a tension of 5 N. Its elongation is x2 under the tension of 7 N. For the elongation of (5x12x2), the tension in the spring will be,         [2025]

1 15 N  
2 20 N  
3 11 N  
4 39 N  

Ans.

(3)

kx1=5 N  x1=5k

kx2=7 N  x2=7k

Then (5x12x2)k=5×52×7=11 N.