Brad tries out a weight-loss plan that involves repeatedly lifting a 48.5-kg barbell from the floor over his head to a height of 1.9 m. If he is able to complete three such lifts per minute, how long will it take for him to lose 0.50 kg of fat? "Burning" 1 g of fat supplies 39 kJ to the body; of this, 10% can be used by the muscles to lift the barbell. (Ignore the fat "burned" while he lowers the barbell to the floor.)

Question

roadjester · Answer

It doesn't say how much "effort" or energy it takes to lift the barbell.

roadjester · Answer

oh wait, never mind

roadjester · Answer

ok, so you've got at 48.5kg barbell.
$F=mg$  and $W=F\Delta x$
This tells you how much energy it will take to lift the barbell.

Now, it tells you "1 g of fat supplies 39 kJ to the body; of this, 10% can be used by the muscles to lift the barbell."

roadjester · Answer

So when you burn 1g of fat, you're supplying 39 X10^3 J of energy to lift the barbell which requires the energy you calculated for the work. I f that makes sense.

anonymous · Answer

ok, I think i get it

roadjester · Answer

Cool.