Q: A block of mass 250g is kept on a vertical spring of spring constant 100 N/m fixed from below. The spring is now compressed to have a length 10cm shorter than its natural length and the system is released from this position. How high does the block rise? Take g = 10 m/s².

(a) 15 cm

(b) 20 cm

(c) 25 cm

(d) 10 cm

Ans: (b)

Sol: $ \displaystyle \frac{1}{2}k x^2 = m g h $

$ \displaystyle \frac{1}{2}\times 100 \times (0.10)^2 = 250 \times 10^{-3}\times 10 \times h $

h = 0.2 m = 20 cm