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Tuesday, October 12, 2010
Ch8 1 #3
Use the rotational analogies for linear motion in constant acceleration. The rotational forms are equations 8.7 - 8.9
6 comments:
Gareth
said...
My numbers are 2s, 3100rev/min. For the second question I converted 3100 rev/min to rev/sec and got 51.67. From there I multiplied by my time (2s) and got 103.33 revolutions. However when I put this in the slot it tells me I'm wrong. What mistake did I make?
The second part of the question is asking for revolutions, not radians... wouldn't you just change the rev/min to rev/sec and then just multiply by the seconds? It's not taking my answer but I can't think where I went wrong
In this case, all that's needed is consistent units. The answer to part (A) is rad/s/s, so either this has to be converted to revs or the final angular velocity has to be in rad/s.
In order to do part two, you have to make sure that you use the same units. This means that when using equation v^2=v0^2+2alpha(deltax), that v and alpha must be the same units. For example, you can make v rpms (which they give you) and then make alpha rev/min^2 (by dividing by 2pi).
6 comments:
My numbers are 2s, 3100rev/min. For the second question I converted 3100 rev/min to rev/sec and got 51.67. From there I multiplied by my time (2s) and got 103.33 revolutions. However when I put this in the slot it tells me I'm wrong. What mistake did I make?
The SI units are rad/sec, not rev/sec. Try an additional conversion step from rev to rad.
I'm having trouble converting from rev/sec to rad/sec... can anyone show me how to do this?
The second part of the question is asking for revolutions, not radians... wouldn't you just change the rev/min to rev/sec and then just multiply by the seconds? It's not taking my answer but I can't think where I went wrong
In this case, all that's needed is consistent units. The answer to part (A) is rad/s/s, so either this has to be converted to revs or the final angular velocity has to be in rad/s.
In order to do part two, you have to make sure that you use the same units. This means that when using equation v^2=v0^2+2alpha(deltax), that v and alpha must be the same units. For example, you can make v rpms (which they give you) and then make alpha rev/min^2 (by dividing by 2pi).
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