Question

if you want to build a container to protect an egg when it is dropped, the surface which touches the egg should be _ in order to _ the time of collision.

a hard, increase
b soft, increase
c soft, decrease
d hard, decrease

Explanation:

When an egg is dropped, the impulse \(I = F\Delta t\) (where \(I\) is impulse, \(F\) is force, and \(\Delta t\) is time of collision) is related to the change in momentum of the egg. The change in momentum \(\Delta p\) (which is related to impulse \(I=\Delta p\)) is fixed for a given drop height (as the initial and final velocities are determined by the drop). To protect the egg (reduce the force \(F\) acting on it), we need to increase the time of collision \(\Delta t\) (since \(F=\frac{\Delta p}{\Delta t}\), for a fixed \(\Delta p\), larger \(\Delta t\) means smaller \(F\)). A soft surface can deform more, which increases the time of collision.

Answer:

B. soft, increase