Question

http://papers.xtremepapers.com/CIE/Cambridge%20International%20A%20and%20AS%20Level/Physics%20(9702)/9702_s03_qp_1.pdf Q22 Please help!

Answer 1

initially, weight goes down a height x, hung on 3 springs.
so change in potential energy = 3 * spring energy (because there are 3 springs)
hence, \[W*x = 3 * 1/2 *k * x^2\]

hence k = 2W/3x

Now, for the new situation, 2W is hung on 2 springs

so, same energy converstion, and let extension be y
\[2W * y = 2 * 1/2 *k * y^2\]

hence y = 2W/k = 3x