# Work & Energy

An elevator cable breaks when a 715 kg elevator is 20.5 m above the top of a huge spring (k = 8.00 104 N/m) at the bottom of the shaft.

(a) Calculate the work done by gravity on the elevator before it hits the spring.

(b) Calculate the speed of the elevator just before striking the spring.

(c) Calculate the amount the spring compresses. (Note that here work is done by both the spring and gravity).

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#### Solution Preview

(a) Calculate the work done by gravity on the elevator before it hits the spring.

m= 715 kg

g= 9.81 m/s^2

h= 20.5 m

Work done= mgh= 143790.08 J =715x9.81x20.5

Answer: work done by gravity on the elevator before it hits the spring.= ...

#### Solution Summary

The solution calculates the work done by gravity on the elevator before it hits the spring, the speed of the elevator just before striking the spring and the amount the spring compresses.