A weight lifter bench‑presses a 160.0 kg 160.0 kg barbell from his chest to a height equal the length of his arms, 0.800 m . 0.800 m. How much work does he do? work: J J What is the potential energy of the barbell relative to the weight lifter's chest after he lifts the barbell? potential energy: J J How many food calories does the weight lifter use if he does this lift 35 times? Assume the weight lifter does no work in letting the barbell drop back to his chest.

A. 1254.4 J

B. 1254.4 J

C. 43904 calories

Explanation:

Parameters given:

Mass of barbell, m = 160 kg

Length of arm, d = 0.8

A. Work done by weight lifter in lifting the barbell is:

W = F * d

Where F is force

F = m * g

=> W = m * g * d

W = 160 * 9.8 *0.8

W = 1254.4 J

B. Potential energy is given as:

PE = m * g * h

Where h is height (in this case, D)

=> PE = m * g * d

PE = 160 * 9.8 * 0.8

PE = 1254.4 J

C. The number of calories the weight lifter uses after lifting the barbell 35 times is equal to 35 times the potential energy, since a calorie is the measure of the amount of potential energy a piece of food contains:

35 * 1254.4 = 43904 calories.

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