“A toolbox of mass $0.70\ \text{kg}$ sits on a trolley of mass $2.1\ \text{kg}$. The trolley rolls without friction and is joined to a fixed post by a spring of $135\ \text{N/m}$. The friction coefficient between toolbox and trolley is $0.32$. The trolley is pulled aside and released. How far can it be pulled before the toolbox slides?” is available to Standard subscribers.