A motor furnishes 120 hp to a device that lifts a 5000-kg load to a height of 13.0 m in a time of 20 s. Find the efficiency of the machine.
The efficiency of a machine, considering the motor delivers a power of
Answer to Problem 10SP
Solution:
Explanation of Solution
Given data:
The power delivered by the motor to the device is
The mass of the lifted load is
The height to which the load was lifted is
The time taken to lift the load to the height is
Formula used:
The formula for efficiency of a machine is
Here,
The work done is calculated by the formula:
Here,
Power is calculated by the formula:
Here,
The formula for weight of a body is
Here,
Explanation:
Consider the expression for weight of the lifted load as
The standard value of
Substitute
Consider the expression for work done to lift the load to a height of
Here,
Substitute
Calculate the power delivered by the machine by the formula:
Here,
Substitute
Consider the expression for efficiency of a machine:
Substitute
Conclusion:
The efficiency of the machine is
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Schaum's Outline of College Physics, Twelfth Edition (Schaum's Outlines)
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