Please help find my error with this velocity diagram?

In summary, the conversation was about finding the piston velocity and angular velocity of AB about A. The homework equations included drawing a velocity vector diagram and using the formula 2∏RPM / 60 to convert crank speed from 3000 rpm to 314.16 rad / s. The attempt at a solution involved drawing a schematic to scale, calculating vectors Voa and Vab, and using the formula Wab = Vab / length ab to find the angular velocity of AB about A. The book's answer for the angular velocity was 21.25 rad/s, but the person calculated it to be 87 rad/s. After consulting with their tutor, it was confirmed that their calculation was correct.
  • #1
LDC1972
65
0

Homework Statement



Find piston velocity and
Find angular velocity AB about A.

Question.jpg


I apologise if the image is poor! If very bad I'll elaborate in writing the values...

Homework Equations



Draw a velocity vector diagram to solve the above.
Also use 2∏RPM / 60 to convert crank speed from 3000 rpm to 314.16 rad / s
And then Wr to get 31.416 metres per sec angular speed of point A
And for "angular velocity AB about A" used Wab = Vab / Length ab = 17.4 / 0.2 = 87 rad / s. (But book says answer should be 21.25??

The Attempt at a Solution



Attached below my 'sketch'. I did this to clarify as well:

This is a simple slider crank example from one of my own books; the book gives the answers but not the method.

The answers given by book are:

34 m/s piston velocity (and I get this right)

21.25rad/s for angular velocity of AB about A. (I get 87 rad/s?)

Please help, question and my space / velocity diagram below.

Basically I did this:

1/ Drew question schematic to scale
2/ Drew Vector Vao (90 degrees to AO)
3/ Drew Vector Vab (90 degrees to AB at piston)
4/ Convert crank rpm to rad/s and then calculate Voa ( Voa = crank rad/s x length 0.1m)
5/ Draw vectors using the angles calculated from above methods (Voa being 30 degrees on right hand side from horizontal)
(Vab being 65 degrees from left hand side horizontal.
6/ Once first vector drawn point A is know, so join next (Vab) to a, and finally measure ao (Vao) to find o, and then drew horizontally across to find b.
7/ Then do Wab = Vab / length ab = 17.4/0.2 = 87 rad/s


Answer vector.jpg

 
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  • #2
It's OK guys - tutor took a look and I am right, the book is wrong!
Thanks though..
 

What is a velocity diagram?

A velocity diagram is a graphical representation of the velocity of a moving object over time. It shows the changes in velocity, including speed and direction, of the object at different points in time.

Why is it important to find errors in a velocity diagram?

Finding errors in a velocity diagram is important because it ensures the accuracy of the data and the reliability of the results. Even small errors can lead to incorrect conclusions and affect the overall validity of a study or experiment.

What are some common errors to look for in a velocity diagram?

Some common errors to look for in a velocity diagram include incorrect data collection, mathematical errors in calculations, and improper labeling or scaling on the graph. It is also important to check for any outliers or anomalies that may skew the data.

How can I check for errors in a velocity diagram?

To check for errors in a velocity diagram, you can compare the data to other sources, such as theoretical calculations or previous experiments. You can also double-check the calculations and labels on the graph, and conduct a thorough review of the data for any inconsistencies.

What are some tips for avoiding errors in a velocity diagram?

To avoid errors in a velocity diagram, it is important to carefully collect and record data, use accurate and precise measurements, and double-check all calculations. It is also helpful to have a colleague review the data and graph for any errors or inconsistencies.

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