Answer:
800
cm²
Explanation:
Given parameters:
radius of the coin = 20cm
Unknown:
Surface area of the coin = ?
Solution:
A coin is made up of two faces;
Surface area = 2(πr²)
Insert the parameters and solve;
Surface area = 2(
)
Surface area = 800cm²
I'll bite:
-- Since the sled's mass is 'm', its weight is 'mg'.
-- Since the coefficient of kinetic friction is μk, the force acting opposite to the direction it's sliding is (μk) times (mg) .
-- If the pulling force is constant 'F', then the horizontal forces on the sled
are 'F' forward and (μk · mg) backwards.
-- The net force on the sled is (F - μk·mg).
(I regret the visual appearance that's beginning to emerge,
but let's forge onward.)
-- The sled's horizontal acceleration is (net force) / (mass) = (F - μk·mg) / m.
This could be simplified, but let's not just yet.
-- Starting from rest, the sled moves a distance 's' during time 't'.
We know that s = 1/2 a t² , and we know what 'a' is. So we can write
s = (1/2 t²) (F - μk·mg) / m .
Now we have the distance, and the constant force.
The total work is (Force x distance), and the power is (Work / time).
Let's put it together and see how ugly it becomes. Maybe THEN
it can be simplified.
Work = (Force x distance) = F x (1/2 t²) (F - μk·mg) / m
Power = (Work / time) = <em>F (t/2) (F - μk·mg) / m </em>
Unless I can come up with something a lot simpler, that's the answer.
To simplify and beautify, make the partial fractions out of the
2nd parentheses:
<em> F (t/2) (F/m - μk·m)</em>
I think that's about as far as you can go. I tried some other presentations,
and didn't find anything that's much simpler.
Five points,ehhh ?
There are a few ways to do this- unfortunately different fields are better at it than others! Medical research is generally pretty good, some other fields likewise very good, some not as much.
Basically, though, what they do is use standadisation- they agree on the terminology, units of data, statistical measures, and so forth, that will be used in that scientific field. As much as possible, every scientist in the field uses those standards so everyone working in the field should recognise it.
For instance, in clinical trials, there is very good agreement worldwide on what the different metrics we use are- e.g. in cancer research, we usually want to know the 5-year survival rate (meaning the percentage of patients still alive 5 years after diagnosis). So anyone with the right training should be able to pick up a clinical trial report and understand what the results are and what the report is saying.
