Question

Brutus, a champion weight lifter, raises 220 kg a distance of 3.10 m. (a) how much work is done by brutus lifting the weights? j (b) how much work is done holding the weights above his head? j (c) how much work is done lowering them back to the ground? j(d) does brutus do work if the weights are let go and fall back to the ground? no yes (e) if brutus completes the lift in 2.1 s, how much power is developed? w

Answer 1

A) work = force * distance 
mass is not a force, weight is, so we have to find the weight of the block. 
Weight = mg 
Weight = (220kg)(9.8) 
Weight = 2156N 
Work = 2156N * 3.10m 
work = 6683.6J 
b) Since he is holding the weights, it's not moving, therefore, he doesn't do any work 
c) The answer is still the same amount of work when he lifted them. 
d) The answer is no since when he let go the weight, he doesn't apply any force to the weight. 
e) P = work/time 
P = 6683.6J / 2.1s 
P = 3182.67 watts