||Homework Help||Kindergarten-University. - Page 8

@Ayeshaa,
For part a, we have to find how many sparks fire in one second.
This means we need sparks/second
Formula is not needed.
Question gives 3.6 * 10^2 r/min and 4 sparks/r
If you multiply them, then r and r will cancel and you are left with sparks/min
You know 1 min = 60 s, therefore you can convert it into sparks/second


In part b, the unit is sparks/second. The second is in denominator, which can be written as second^-1 which I shortened to s^-1. We can skip "sparks" because we already know that we are talking about sparks.

Edited by akhl - 12 years ago

@Ayeshaa,
Another way to understand part a is
3.6 * 10^2 revolutions in 1 min
Or, 3.6 * 10^2 revolutions in 60 s
Therefore, 1 revolution in 60/(3.6*10^2) s i.e. 1/6 s
Also, 4 sparks fire in 1 revolution

Therefore, in 1/6 s, 4 sparks fire
In 1 s, 4 * 6 = 24 sparks fire

Another way to understand part b is
24 sparks fire in one second.
This means after a spark has fired, 24 more sparks will fire in 1 second.
Therefore, after a spark has fired, 1 more spark will fire in 1/24 second
Therefore, time between two sparks = 1/24 second

I can also help with Spanish, Math (especially Algebra and Geometry), and English. Know a little 'bout US History. Edited by -Shankar- - 12 years ago

Thanks so much for this explanation:) I get confused very easily, and then soo many questions arise in my head, so thank you very much for simplifying your words, and giving me a better understanding of how you worked this problem out:)

@Shankar Edited by _Jess_ - 12 years ago

Physics Question out of Textbook:

@Ayeshaa, the correct answer is

1. The football is kicked so that the line of force of the kick passes through the CM (center of mass) of the football.

2. When the football is thrown without giving it any spin.

In these cases, the motion of the football can be simplified to the motion of its CM.


The football cannot be treated as a reference point if

either

1. the line of action of the force of the kick does not pass through the CM

or

2. a spin is given when throwing the football.


In either of these cases, the football has rotational motion (together with translational). But, to replace the football by a point, we need only translational motion because rotational motion makes no sense for a reference point.



Edited by akhl - 12 years ago

^^ Thanks so much =) Edited by -Ayeshaa- - 12 years ago

Well it doesn't really give you much information, I think that the displacement would be 0 for both.