A man drinks a bottle of beer and proposes to work off its 460 kj by exercising with a 20 kg barbell. If each lift of the barbell from chest height to over his head is through 60 cm and the efficiency of his body is 10 percent under these circumstances, how many times must he lift the barbell?
Solve this equation:
(Energy consumed) * 0.10 = Work done
(460*10^3 J)* 0.10 = (number of lifts) * (M g)* (0.60 m)
M = 20 kg and g = 9.80 m/s^2.
Solve for the number of lifts
For some reason not getting it.
I gave you the equation to solve for the number of lifts, and told you what M and g are in the equation. The rest is just doing the numbers.
67
To answer this question, we need to calculate the amount of work done in lifting the barbell and then find out how many times it needs to be lifted in order to work off the energy from the bottle of beer.
First, let's calculate the work done in lifting the barbell. The work done is given by the formula:
Work = Force × Distance × Efficiency
The force required to lift the barbell can be calculated using Newton's second law, which states that force (F) is equal to mass (m) multiplied by acceleration due to gravity (g).
Force = mass × acceleration due to gravity
Force = 20 kg × 9.8 m/s^2
Force = 196 N
The distance through which the barbell is lifted is given as 60 cm, which is equal to 0.6 meters.
Now, let's calculate the work done:
Work = 196 N × 0.6 m × 0.1 (10% efficiency)
Work = 11.76 J (joules)
Now, let's calculate the energy provided by the bottle of beer, which is given as 460 kJ. Since 1 kJ (kilojoule) is equal to 1000 J (joules), we have:
Energy from beer = 460 kJ × 1000 J/kJ
Energy from beer = 460,000 J
Next, let's find out how many times the barbell needs to be lifted to work off this energy.
Number of lifts = Energy from beer ÷ Work done per lift
Number of lifts = 460,000 J ÷ 11.76 J
Number of lifts = 39,146.9 (approx.)
Therefore, the man needs to lift the barbell approximately 39,147 times to work off the energy from the bottle of beer.