Work power and energy by a weight lifter

[ridsyfootball]

Homework Statement

A weight lifter (mass 75Kg) raises body's centre of mass by 0.4 in the process of lifting a barbell weight of 70kg to the height of 1.04m above the ground. Calculate the total work done in lifting the weight.The weight is raised in 0.2 seconds; hence calculate the power of the weight lifter.

Homework Equations

m x a = f
F x s = work
Power= work done/time taken

The Attempt at a Solution

70kg X 9.81 m/s = 686.7N
work= 686.7 X 1.04=714.168 j
How do i work out the distance travelled? the weight lifter wouldn't lift a barbell 1.04m.
power =714.168/0.2=1373.4 W

 

[tiny-tim]

welcome to pf!

hi ridsyfootball! welcome to pf!

… How do i work out the distance travelled? the weight lifter wouldn't lift a barbell 1.04m.

i don't understand … that's about chest-height … what's worrying you about that?

(and don't forget to add the work done by raising his own mass )

 

[cupid.callin]

sorry my first post was deleted as i gave u a straight answer
so,

write the coordinates of CM before and after lifting the weight

solve them and u can het the answer

 

[ridsyfootball]

thanks for the help guys i understand now and iv got what i think is the correct answer.