Question

A weightlifter is bench-pressing 710 N. He raises the weight 0.65m above his chest. How much work does he do with this lift?

Answer 1

The work done is 461.5 J.

Explanation:

According to Kinetics, the work done is calculated as the product of force which has done work, and the displacement it has imposed. Hence,

                     $\text {Work done}=F \times s$

In the problem, the given data, F = 710 N and s = 0.65 m

By applying the given values to the work done equation, we get as follows,

                     $\text { Work done } = 710 \times 0.65 = 461.5 \mathrm{J}$

The unit is same as the energy, work done defines when 1 N force acts in a 1 m distance along the force’s direction.

Answer 2

The work done is 6958 J

Explanation:

The work done by the man to raise the weight is the equal to the increase in gravitational potential energy of the weight, so we can write:

$W=mg \Delta h$

where

(mg) is the weight, with m being the mass and g the acceleration of gravity

$\Delta h$ is the change in height of the weight

In this problem, we have

mg = 710 N (weight)

$\Delta h = 0.65 m$

Therefore, the work done is

$W=(710)(9.8)=6,958 J$

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