Work = (weight) x (distance)
Work = (50 lb) x (1 kg / 2.20462 lb) x (9.81 newton/kg)
x (4 feet) x (1 meter / 3.28084 feet)
= (50 x 9.81 x 4) / (2.20462 x 3.28084) newton-meter
= 271.3 joules .
We don't need to know how long the lift took, unless we
want to know how much power he was able to deliver.
Power = (work) / (time)
= (271.3 joule) / (5 sec) = 54.3 watts .
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The easy way:
Work = (weight) x (distance)
= (50 pounds) x (4 feet) = 200 foot-pounds
Look up (online) how many joules there are in 1 foot-pound.
There are 1.356 joules in 1 foot-pound.
So 200 foot-pounds = (200 x 1.356) = 271.2 joules.
That's the easy way.
