Hacked off with college over Velocity Ratio and Efficiency question.

Click For Summary
SUMMARY

The discussion centers on calculating the useful energy output given an input of 3000 joules, using the concepts of Velocity Ratio (VR) and Mechanical Advantage (MA). The user, Rich, calculated VR as 0.17 and MA as 0.17, leading to an efficiency of 100%. Despite this calculation, Rich faced criticism for claiming 100% efficiency, as it is widely accepted that real-world systems cannot achieve this due to factors like friction. The lack of a specified friction variable in the question is a point of contention.

PREREQUISITES
  • Understanding of basic physics concepts such as work, energy, and efficiency.
  • Familiarity with the formulas for Velocity Ratio (VR) and Mechanical Advantage (MA).
  • Knowledge of how to calculate efficiency in mechanical systems.
  • Ability to interpret and analyze physics problems involving angles and forces.
NEXT STEPS
  • Study the impact of friction on mechanical efficiency in real-world applications.
  • Learn about the principles of energy conservation and its implications in physics problems.
  • Explore advanced topics in mechanical advantage and how they apply to different machines.
  • Review case studies that illustrate common misconceptions in efficiency calculations.
USEFUL FOR

This discussion is beneficial for physics students, educators, and anyone interested in understanding the principles of mechanical efficiency and the implications of theoretical versus practical calculations in physics.

RichMortimer
Messages
26
Reaction score
0

Homework Statement



If the work put in is 3000j, calculate the useful energy output.

[PLAIN]http://www.mkwebman.com/question

Load = 1962N

Homework Equations



VR = Distance covered by effort / Distance covered by load
MA = load/effort
Efficiency = MA / VR
Efficiency = useful output energy / input energy

The Attempt at a Solution



I firstly worked out the distance moved vertically by both the effort and load. These are 0.71 for the effort and 4.24 for the load based on an angle of 45 degrees.

VR = 0.71/4.24 VR = 0.17

MA = 1962/11772 MA = 0.17

As the question doesn't mention friction I've used efficiency = MA/VR.

efficiency = 0.17/0.17
efficiency = 1 1 x 100 = 100%

Finally, using efficiency = useful output energy / input energy

useful output = 1 x 3000

Useful = 3000j


I've been told I'm wrong as it cannot be 100% efficient. However, as the question doesn't state a friction variable and which ever ratio I use returns 0.17 I can't see how this is marked incorrect!


Please please help if you can.

Thanks in advance,

Rich.
 
Last edited by a moderator:
Physics news on Phys.org
There is a problem viewing your attached image.
 
it is at www.mkwebman.com/question[/URL]

Thank you!
 
Last edited by a moderator:

Similar threads

Engineering Velocity Ratio, mechanical advantage, Efficiency of a screw jack
  • · Replies 1 ·
Replies
1
Views
10K
Effort/ Load simple machines question
  • · Replies 2 ·
Replies
2
Views
2K
Simple Gear Train Efficiency and Torque Help
  • · Replies 26 ·
Replies
26
Views
23K
Velocity Ratio of a 3rd Class Lever
  • · Replies 11 ·
Replies
11
Views
5K
How Does Efficiency Impact Velocity Ratio in a Third Class Lever?
  • · Replies 2 ·
Replies
2
Views
11K
What Calculations Are Needed to Solve This Third Order Lever Problem?
  • · Replies 1 ·
Replies
1
Views
5K
How Does Mark-Space Ratio Affect Boost Converter Performance?
  • · Replies 9 ·
Replies
9
Views
3K
Velocity ratio of a third class lever
  • · Replies 9 ·
Replies
9
Views
14K
Dynamics assignment, power output of car
  • · Replies 7 ·
Replies
7
Views
2K
What is the most efficient way to solve a wheel and axle system problem?
  • · Replies 15 ·
Replies
15
Views
11K