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.

 

[rwisz]

I would like to clarify some assumptions and considerations in the given scenario. First, it is important to note that the calculation of work done involves the displacement of the object, not the distance traveled by the weight lifter. In this case, the displacement is the change in height of the barbell (1.04m), not the distance traveled by the weight lifter.

Secondly, the calculation of power also requires the time taken to perform the work. In this case, it is given that the weight is raised in 0.2 seconds, which can be used to calculate the power of the weight lifter.

Therefore, the total work done by the weightlifter can be calculated as follows:

Work = Force x Displacement = (70kg x 9.81m/s^2) x 1.04m = 714.168 Joules

The power of the weight lifter can be calculated as follows:

Power = Work done/Time taken = 714.168 J / 0.2 s = 3570.84 Watts

In conclusion, the weight lifter has exerted a force of 686.7N to lift the barbell weighing 70kg to a height of 1.04m, resulting in a total work done of 714.168 Joules and a power of 3570.84 Watts in 0.2 seconds. It is important to note that these calculations are based on the given scenario and may vary in real-life situations due to other factors such as the weight lifter's technique and the dynamics of the movement.