[填空题]
An elevator cable breaks when a 920-kg ele5e4e/gknot-d rlpfk bkc0 7hxm p::938hy,va vat)) zeca zz,2ovor is 28 m above a huge spring ($k=2.2\times10^{5} \mathrm{N/m}$) at the bottom of the shaft. Calculate
(a) the work done by gravity on the elevator before it hits the spring,$\approx$ j
(b) the speed of the elevator just before striking the spring,$\approx$ m/s
(c) the amount the spring compresses (note that work is done by both the spring and gravity in this part). m
