What work does a person need to do in order to lift a 9 kg bucket of water from a well 30 m
What work does a person need to do in order to lift a 9 kg bucket of water from a well 30 m deep with the help of a gate with an efficiency of 90%?
1. Let’s write down the condition:
S = 30 m
m = 9 kg
Efficiency = 90% = 0.9
A-?
2. Let’s compose a formula for finding useful work, taking the weight of a bucket of water as the force:
A floor. = F × S
F = P
P = mg
A floor. = mg × S
3. Substitute into the formula the numbers from the condition:
A floor. = 9 kg × 10 N / kg × 30 m
A floor. = 2700 J
4. From the efficiency formula, we derive the formula for finding the work expended and find the numerical answer:
Efficiency = A pol. / A zat.
A zat. = A pol. / Efficiency
A zat. = 2700 J / 0.9
A zat. = 3000 J
5. Let’s correlate the number with the answers and choose the correct one:
The answer is 2.