Help with questions on ASTB Mechanical Flashcards

[irish08slasher]

So I'm currently reviewing the flashcards and have come across a problem that I cannot get the right answer to. The question is as follows.

A 5 kg wad of clay is tied to the end of a string. A 300 gm copper moving horizontally is embedded into the clay and causes the clay and ball to rise to a height of 0.2 m. The intial velocity v¹ of the ball is nearly


6.3 m/s

7.3 m/s

8.3 m/s

The answer given is 8.3 m/s

From my understanding, this seems to be a question about Kinetic Energy= Potential Energy. With that in mind, I jot out the Potential Energy and solve for velocity and while my best answer is 8.08 m/s I can't get 8.3. I've tried reworking the problem multiple times, checking for errors, but I still come across the same error. Am I completely off track or am I just making a minor miscalculation?

 

[Hopeful Hoya]

I came across this in my studies, seems like you already took the OAR but figured I'd post it for anyone else who had trouble figuring it out (as I did).

You were right setting PE=KE, so the equation should have been (.5)*(.3)*v^2 = (5.3)*(9.8)*(.2). The math is pretty annoying to do by writing it out, so I would assume that's where something went amiss.

Just out of curiosity, did you come across any problems on the ASTB that required such large amounts of old-fashioned long multiply and divide math?

 

[irish08slasher]

I came across this in my studies, seems like you already took the OAR but figured I'd post it for anyone else who had trouble figuring it out (as I did).

You were right setting PE=KE, so the equation should have been (.5)*(.3)*v^2 = (5.3)*(9.8)*(.2). The math is pretty annoying to do by writing it out, so I would assume that's where something went amiss.

Just out of curiosity, did you come across any problems on the ASTB that required such large amounts of old-fashioned long multiply and divide math?

The only math intensive problems I encountered were in calculating force and finding Resistance in electrical currents, but that was nowhere as complex as this. In my version, the Mechanical section of the test was mostly "Do you know what this is taking about? If so, write the correct answer, if not, move on."It was a simple matter of either knowing what it was talking about or not, so brush up on your physics. The worst question I got was something about nuclear reactions, I guessed on that one and moved on.

 

[nightflaw]

From what I remember (took the ASTB late last year) the mechanical section was MUCH easier than I was expecting. If you are comfortable with the AW study guide, you should have no problems.