Mechanical Engineering Exam  >  Mechanical Engineering Questions  >  Mechanical efficiency of a certainengine is 7... Start Learning for Free
Mechanical efficiency of a certain engine is 75% and it develops a brake power of 40 kW. What will be the new mechanical efficiency at half load if friction power is assumed to be constant?
  • a)
    65%
  • b)
    40%
  • c)
    60%
  • d)
    58%
Correct answer is option 'C'. Can you explain this answer?
Verified Answer
Mechanical efficiency of a certainengine is 75% and it develops abrake...
View all questions of this test
Most Upvoted Answer
Mechanical efficiency of a certainengine is 75% and it develops abrake...
Question:

Mechanical efficiency of a certain engine is 75% and it develops a brake power of 40 kW. What will be the new mechanical efficiency at half load if friction power is assumed to be constant?

Solution:

Given,
Mechanical efficiency of the engine, η1 = 75%
Brake power developed by the engine, P1 = 40 kW

Let,
Friction power of the engine, Pf = Constant
Load on the engine, L2 = L1/2

We know that,
Mechanical efficiency = Output power / Input power

Output power = Brake power – Friction power
Input power = Indicated power

Indicated power = Brake power / Mechanical efficiency

At full load (L1),
η1 = Output power1 / Input power1
Input power1 = Brake power / η1
Input power1 = 40 / 0.75
Input power1 = 53.33 kW

Output power1 = Brake power1 – Friction power

At half load (L2),
Input power2 = Input power1 / 2
Input power2 = 53.33 / 2
Input power2 = 26.67 kW

Output power2 = Input power2 x η2
η2 = Output power2 / Input power2

At half load,
Output power2 = Brake power2 – Friction power
Brake power2 = L2 x BP1 / L1

Brake power2 = (1/2) x 40
Brake power2 = 20 kW

Output power2 = 20 – Pf

η2 = Output power2 / Input power2
η2 = (20 – Pf) / 26.67

Therefore, the new mechanical efficiency at half load if friction power is assumed to be constant is 60%.
Attention Mechanical Engineering Students!
To make sure you are not studying endlessly, EduRev has designed Mechanical Engineering study material, with Structured Courses, Videos, & Test Series. Plus get personalized analysis, doubt solving and improvement plans to achieve a great score in Mechanical Engineering.
Explore Courses for Mechanical Engineering exam

Top Courses for Mechanical Engineering

Mechanical efficiency of a certainengine is 75% and it develops abrake power of 40 kW. What willbe the new mechanical efficiency athalf load if friction power isassumed to be constant?a)65%b)40%c)60%d)58%Correct answer is option 'C'. Can you explain this answer?
Question Description
Mechanical efficiency of a certainengine is 75% and it develops abrake power of 40 kW. What willbe the new mechanical efficiency athalf load if friction power isassumed to be constant?a)65%b)40%c)60%d)58%Correct answer is option 'C'. Can you explain this answer? for Mechanical Engineering 2024 is part of Mechanical Engineering preparation. The Question and answers have been prepared according to the Mechanical Engineering exam syllabus. Information about Mechanical efficiency of a certainengine is 75% and it develops abrake power of 40 kW. What willbe the new mechanical efficiency athalf load if friction power isassumed to be constant?a)65%b)40%c)60%d)58%Correct answer is option 'C'. Can you explain this answer? covers all topics & solutions for Mechanical Engineering 2024 Exam. Find important definitions, questions, meanings, examples, exercises and tests below for Mechanical efficiency of a certainengine is 75% and it develops abrake power of 40 kW. What willbe the new mechanical efficiency athalf load if friction power isassumed to be constant?a)65%b)40%c)60%d)58%Correct answer is option 'C'. Can you explain this answer?.
Solutions for Mechanical efficiency of a certainengine is 75% and it develops abrake power of 40 kW. What willbe the new mechanical efficiency athalf load if friction power isassumed to be constant?a)65%b)40%c)60%d)58%Correct answer is option 'C'. Can you explain this answer? in English & in Hindi are available as part of our courses for Mechanical Engineering. Download more important topics, notes, lectures and mock test series for Mechanical Engineering Exam by signing up for free.
Here you can find the meaning of Mechanical efficiency of a certainengine is 75% and it develops abrake power of 40 kW. What willbe the new mechanical efficiency athalf load if friction power isassumed to be constant?a)65%b)40%c)60%d)58%Correct answer is option 'C'. Can you explain this answer? defined & explained in the simplest way possible. Besides giving the explanation of Mechanical efficiency of a certainengine is 75% and it develops abrake power of 40 kW. What willbe the new mechanical efficiency athalf load if friction power isassumed to be constant?a)65%b)40%c)60%d)58%Correct answer is option 'C'. Can you explain this answer?, a detailed solution for Mechanical efficiency of a certainengine is 75% and it develops abrake power of 40 kW. What willbe the new mechanical efficiency athalf load if friction power isassumed to be constant?a)65%b)40%c)60%d)58%Correct answer is option 'C'. Can you explain this answer? has been provided alongside types of Mechanical efficiency of a certainengine is 75% and it develops abrake power of 40 kW. What willbe the new mechanical efficiency athalf load if friction power isassumed to be constant?a)65%b)40%c)60%d)58%Correct answer is option 'C'. Can you explain this answer? theory, EduRev gives you an ample number of questions to practice Mechanical efficiency of a certainengine is 75% and it develops abrake power of 40 kW. What willbe the new mechanical efficiency athalf load if friction power isassumed to be constant?a)65%b)40%c)60%d)58%Correct answer is option 'C'. Can you explain this answer? tests, examples and also practice Mechanical Engineering tests.
Explore Courses for Mechanical Engineering exam

Top Courses for Mechanical Engineering

Explore Courses
Signup for Free!
Signup to see your scores go up within 7 days! Learn & Practice with 1000+ FREE Notes, Videos & Tests.
10M+ students study on EduRev