A running track at Harvard University uses a surface with a force constant of 2.5 × 105 N / m. This surface is compressed slightly every time a runner's foot lands on it. The force exerted by the foot, according to the Saucony shoe company, has a magnitude of 2700 N for a typical runner. Treating the track's surface as an ideal spring, find

(a) The amount of compression caused by a foot hitting the track

(b) The energy stored briefly in the track every time a foot lands.