A person running in place on an exercise machine for 10 min uses up 17 kcal (food calories). Another person exercises by repeatedly lifting two 2.5-kg weights a distance of 50 cm. How many repetitions of this exercise are equivalent to 10 minutes of running in place? Assume that the person uses negligible energy in letting down the weights after each lift. (1 cal = 4.186 J)

The number of repetitions of exercise = 56856

Explanation:

Work done or potential by the person lifting a weight = mgh

Where m = mass of the the weight (N), g = acceleration due to gravity (m/s²)

h = Height (m)

m = 2.5 Kg,

h = 50 cm

conversion: cm to m = 50/100 = 0.5 m

∴ Work done = 2.5 * 0.5 = 1.25 J

Work done by the person lifting a weigh = 1.25 J

4.186 J = 1 cal

∴ 1.25 J = (1 * 1.25) / 4.186 = 0.299 cal.

If the first person uses up 17 Kcal in 10 min.

⇒ 17 * 10³ cal in 10 min = 17000 cal in 10 min

The number of repetitions of exercise = 17000/0.299

∴The number of repetitions of exercise = 56856