A weightlifter works out at the gym each day. Part of her routine is to lie on h

Question

A weightlifter works out at the gym each day. Part of her routine is to lie on her back and lift a 45 kg barbell straight up from chest height to full arm extension, a distance of 0.50 m . All answers are in J. Part A How much work does the weightlifter do to lift the barbell one time? Express your answer using two significant figures. Part B If the weightlifter does 24 repetitions a day, what total energy does she expend on lifting, assuming a typical efficiency for energy use by the body (25%). Express your answer using two significant figures. Part C How many 500 Calorie donuts can she eat a day to supply that energy? Express your answer using two significant figures.

Explanation / Answer

A weightlifter works out at the gym each day. Part of her routine is to lie on her back and lift a 45 kg barbell straight up from chest height to full arm extension, a distance of 0.50m.

(A) How much work does the weightlifter do to lift the barbell one time?
Work = force * distance
Weight = 45 * 9.8 =441 N
Work = 45 * 9.8 * 0.5 = 220.5 N-m = 220.5 J

(B) If the weightlifter does 24 repetitions a day, what total energy does she expend on lifting? Assume 25% efficiency.
Work = Energy
Energy =220.5 J /rep * 24 rep = 5292 J if 100% efficiency
Since she is only 25% efficient, she has to expend 4 * 5292 J = 21,168 J of energy to do 5292 J of work.

(C) How many 500 Calorie donuts can she eat a day to supply that energy?
4.18 J = 1 calorie
21168 J ÷ 4.18 J/cal = 5064.11 calories ÷ 500 cal /donut = 10.13 donuts

Related Questions

Navigate

• Browse (All)
• Browse A
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.