## physics ch.1 passage Q2

mcatacct1
Posts: 65
Joined: Sat Oct 26, 2019 4:35 pm

### physics ch.1 passage Q2

I have issues with this problem...

1) Without knowing that flexion-devation (Y axis) and planar radioulnar devation (X axis) are operating at the same velocity I don't see how you can do this problem?

If A is faster than H then C is entirely possible.
If A and H are equal in velocity then I say the x-component is only contributed by H. So I could eliminate C on those grounds and go with the most vertical option between E,F, G.

But I could also say the A component is larger than the H component and just go with the most vertical choice (option C).

2) I also don't see how we can solve this problem without being told the entire wrist motion is ~5 seconds.

If the wrist motion is <5 seconds the X component of the resultant vector should be less than the X component from vector H and that leaves only option C.
If the wrist motion is =5 seconds the x component of the resultant vector should be equal to H and that leaves E,F, and G. But the vertical component should be A+H*sin(5 degrees), which is larger than our value.

3) I saw this post...viewtopic.php?t=1764

I don't see where we derive the idea that we need a vector less than 45 degrees from vector A.

If possible, could you elaborate specifically what information I was suppose to extract, infer, and apply to solve this problem? I sat with this problem for a while, and I really don't get it.
NS_Tutor_Mathias
Posts: 616
Joined: Sat Mar 30, 2019 8:39 pm

### Re: physics ch.1 passage Q2

I don't like to unnecessarily disparage any of the older book materials as many of them have their merits, but rest assured everybody involved in this passage has been taken to the dedicated Blueprint Next Step whipping shed and disciplined thoroughly. This does not represent the quality of the majority of our materials, and I would at this point recommend disregarding this entire passage in favor of online physics practice from our QBank.

1) Angular velocity follows the same rules as linear velocity, so the change in theta over the change in time would give the average angular velocity. Angular vector addition likewise would work the same way. Despite this, I feel the graphical representation and notation here is more than a little lacking.

2) The entire wrist motion seems to be 9.9 seconds. Durations for each are given. But again, seeing as this motion isn't necessarily within the same plane (the two planes indicated are orthogonal to each other, best I can tell), I feel that the graphical representation here doesn't lend itself to meaningful vector addition.
mcatacct1
Posts: 65
Joined: Sat Oct 26, 2019 4:35 pm

### Re: physics ch.1 passage Q2

Okay, thanks so much! The forum in conjunction with the books has been a great resource.