A weightlifter has a basal metabolic rate of 74.8 W. As he is working out, his m

Question

A weightlifter has a basal metabolic rate of 74.8 W. As he is working out, his metabolic rate increases by about 650 W (a) How many hours does it take him to work off a 450 Calorie bagel if he stays in bed all day? (b) How long does it take him if he's working out? (c) Calculate the amount of mechanical work necessary to lift a 99 kg barbell 2.30 m. (d) He drops the barbell to the floor and lifts it repeatedly. How many times per minute must he repeat this process to do an amount of mechanical work equivalent to his metabolic rate increase of 650 W during exercise? (e)Could he actually do repetitions at the rate found in part (d) at the given metabolic level?

Explanation / Answer

a) 450 Cal = 450000 cal
so we need to convert the calories to joules by multiply by 4.184 and then divide by the watts

t= 450000*4.184/74.8
t=25171 seconds= 7 hours

b) we do the same thing by divide by the adjusted metabolic wattage
t= 450000*4.184/(74.8+650)
t=.72 hours

c) work is the product of force and distance:
W=fd
W=mgd
W=99(9.8)(2.3)
W=2231.46 joules

d) knowing that he average 650 joules/ sec we can multiple by 60 to get the amount of joules per minute. 39000 joules/ min. So now that we know the rate per minute and the amount of joules per lift, we can calculate the lifts per minute to achieve this rate

n=39000/2231.46
n=17.48 lifts/minute

(a lift and drop every 3.4 seconds)
e) seems doable for a short stretch but extremely difficult to maintain over an substantial time period

hope that helps

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