Question

All answers must be completely reduced and simplified for full credit. Show all work necessary to complete the problem. (Use a calculator for calculating if you need to.) 1. (3 points) How much work is done when a hoist lifts a 150-kg boulder to a height of 8m? 2. Suppose that 6 J of work is needed to stretch a spring from its natural length of 20cm to a length of 28 cm. a) (4 points) How much work is needed to stretch the spring from 22 to 25 cm? b) (3 points) How far beyond its natural length will a force of 20N keep the spring stretched?

Answer 1

Worek done in lifting a med body of mass on to a height " magah g-acceleration due to gravity =9.8 m/s² where = kg Here m= 150 h28m Work done w = mgh - 150 X 9.8 X 8 11760 J e 11.76 kJ Worek needed to Stretch a Sprung from lts natural length of 20cm to 28cm = 6] According to Hooke's law = 2 K x² K = 6x2 (0.0812 - 1875 N/m a) Worek needed to stretch the spring from 22 cm to 25cm = 1 K 2 2 - 1 k ni tl K (22-2) where x, = 0.02m x2 = 0.05m, as natural length 20cm W = 1 x 1875[(0.05²_10.02) - 1.97]

K=1875 N/m 6) F = kon -QON x = 20 = 0.01 m = 1cm 18.75 So, a force of 20N will keep the spring streetched 1 cm beyond its naturcal length.