Efficiency Calculation for Mechanical System with Incomplete Information

In summary, the conversation discusses a problem with finding the efficiency of an elevator that raises 30 people per minute and has a load of 70 kg. The potential energy and power of the elevator are calculated, and it is determined that the efficiency is 87.3%. The conversation also mentions the need to match up time units and the concept of useful work.
  • #1
TyErd
299
0

Homework Statement


Hey I've attached the question. My main problem is figuring out how to start.


Homework Equations


not exactly sure, PE=mgh?
efficiency= used power/total power *100 = used power/ 2950 * 100...


The Attempt at a Solution


i calculated the potential energy 70*30*9.81*7.5=154507.5 J
I thought about finding the angle of elevation but don't have enough information.
 

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  • #2
TyErd said:

Homework Statement


Hey I've attached the question. My main problem is figuring out how to start.


Homework Equations


not exactly sure, PE=mgh?
efficiency= used power/total power *100 = used power/ 2950 * 100...


The Attempt at a Solution


i calculated the potential energy 70*30*9.81*7.5=154507.5 J
I thought about finding the angle of elevation but don't have enough information.

You will need to match up your time units for a start.

Watts is Joules per second. but the load is 30 people per minute.
 
  • #3
The work done by the elevator raised the people; increased their potential energy. Is that useful work?
That happened in 1 minute. What was the power ?

ehild
 
  • #4
okay I've matched up time units. 2950 J/s and 0.5 people/ second.
potential for half a person? = 35*9.81*7.5 = 2575.125 J/s is that right??
 
  • #5
It is right.ehild
 
  • #6
so then to find efficiency i just do 2575.125/2950 * 100 = 87.3%?
 
  • #7
TyErd said:
so then to find efficiency i just do 2575.125/2950 * 100 = 87.3%?

Yes.

ehild
 

Related to Efficiency Calculation for Mechanical System with Incomplete Information

1. What is mechanical efficiency problem?

Mechanical efficiency problem refers to the loss of energy in a mechanical system due to friction, heat, and other factors that reduce the output compared to the input.

2. How is mechanical efficiency calculated?

Mechanical efficiency is calculated by dividing the output energy by the input energy, and then multiplying by 100 to get a percentage. It can also be calculated by dividing the work output by the work input.

3. What factors affect mechanical efficiency?

Factors that affect mechanical efficiency include friction, heat, wear and tear of parts, misalignment, and other forms of energy loss in a mechanical system.

4. Why is mechanical efficiency important?

Mechanical efficiency is important because it affects the overall performance and effectiveness of a mechanical system. It can also impact the cost and energy consumption of the system.

5. How can mechanical efficiency be improved?

Mechanical efficiency can be improved by using high-quality materials, proper lubrication and maintenance, reducing friction, and optimizing the design and alignment of the mechanical system.

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