Question

A weightlifter expends 294 w of power lifting a weight to a height of 2 m in 10 seconds. what mass has he lifted?

Answer 1

The power of the weightlifter is equal to the ratio between the work done by it and the time taken:
$P= \frac{W}{t}$
since we know the power and the time, we can find the work done:
$W=Pt=(294 W)(10 s)=2940 J$

For the work-energy theorem, this work done by the lifter is equal to the gravitational potential energy gained by the mass, which is given by:
$U=mg \Delta h$
where m is the mass and $\Delta h$ is the increase in height. Rearranging the formula and using W=U, we can find the mass:
$m= \frac{U}{g\Delta h}= \frac{2940 J}{(9.81 m/s^2)(2 m)}=149.8 kg$