A weightlifter works out at the gym each day. Part of her routine is to lie on her back and lift a 42 kg barbell straight up from chest height to full arm extension, a distance of 0.48 m.

a. How much work does the weightlifter do to lift the barbell one time?
b. If the weightlifter does 23 repetitions a day, what total energy does she expend on lifting, assuming a typical efficiency for energy use by the body?
c. How many 500 Calorie donuts can she eat a day to supply that energy?

Explanation

A)   Work done for one time = Force x distance

Mass = 42 kg

Acceleration = 9.81 m/s

Distance = 0.48m

B) Work done = Energy

     Total Energy for 23 repetitions will have to do with the total distance covered within that amount of repetition. A full cycle from her chest and back to her chest will have a total distance of  0.48 m multiply by 2 which gives 0.98 m. Therefore for 23 repetition, we have 0.98 m multiply by 23 and this gives 22.08 meter in total.

C)  1 calories is equal to 4.184J

     there 500 calories is equal to 2092 J

   Therefore four (4) of 500 calorie donuts can supply the needed energy of 2092j.