1:question A weight W is suspended from a rigid support by a hard spring with stiffness constant k . The spring is enclosed in a hard plastic sleeve, which prevents horizontal motion, but allows vertical oscillations. A simple pendulum of length l with a bob of mass m (mg<<W) is suspended from the weight W and is set oscillating in a horizontal line with a small amplitude. After some time has passed, the weight W is observed to be oscillating up and down with a large amplitude (but not hitting the sleeve). It follows that the stiffness constant k must be: k=4w/l k=2w/l k=w/l k=w/2l ans:1 2:relevant equations w^2=k/m 3:attempt Please hint me where to start. I tried balancing the forces but that brought me nowhere.