Question

A weight lifter is bench-pressing a barbell whose weight is 710 N. He raises the barbell a vertical distance of 0.65 m, and then lowers it back to its original position next to his chest. Assume the weight is raised and lowered at a constant velocity, and that “up” is the positive direction. Determine the work done on the barbell (a) While the barbell is being raised (b) While the barbell is being lowered

Answer 1

here,

weight of the babell , w = 710 N

height , h = 0.65 N

(a)

the work done while the barbell is being raised , workdone = w*h

workdone = 710 I0.65

workdone = 461.5 J

the workdone while the barbell is being raised is 461.5 J

(b)

the work done while the barbell is being lowered , workdone = - w*h

workdone = - 710 I0.65

workdone = - 461.5 J

the workdone while the barbell is being lowered is - 461.5 J