Question

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?

Answer 1

Step-by-step explanation

A) Work done for one time = Force x distance

• Force = mass x acceleration

Mass = 42 kg

Acceleration = 9.81 m/s

Distance = 0.48m

• Work done = mass x acceleration x distance
• Work done = 42 x 9.81 x 0.48 = 197.77 kg
  `m^(2)`/s = 197.77J

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.

• Total Energy in achieving 22.08 meter = mas x acceleration x distance

• Total Energy in achieving 22.08 m = 42 x 9.81 x 22.08 = 9097 J

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.