Question

An athlete needs to lose weight and decides to do it by “pumping iron.” (a) How many times must an 82.0 kg weight be lifted a distance of 0.720 m in order to burn off 1.00 lb of fat, assuming that that much fat is equivalent to 3500 kcal? (b) If the weight is lifted once every 1.80 s, how long does the task take?

Answer 1

Let the weight be m, and the distance be h.

For every lift, the athlete is doing work equivalent to the potential energy required for the weight to be at height h, which is mgh. Where g is the gravitational acceleration.

Let the number of times the athlete lifts the weight is n.

Then

(using 1 kcal = 4184 Jule)

Wtih m= 82 kg

h=0.72 m,

g=10 m s^-2

a) The wight must be lifted 24804 times.

To answer the second part, if each lift takes an amount 1.8 seconds,

24804 lifts will take (24804*1.8)=44647.2 sec or 12.4 Hours.

b)The task will take 44647.2 sec or approx 12.4 hrs.