Sattelites don't need any fuel to stay in orbit. The applicable law is...."objects in motion tend to stay in motion". Having reached orbital velocity, any such object is essentially "falling" around the earth. Since there is no (or at least very little) friction in the vacuum of space, the object does not slow.... It simply continues.
Sattelites in "low" earth orbit do encounter some friction from the very thin upper atmosphere, and they will eventually "decay".
:)
I notice that even though we're working with frames of reference
here, you never said which frame the '5 km/hr' is measured in.
In fact ! You didn't even say which frame the '12 km/hr' of his
bike is measured in.
So there are several different ways this could go. I'll do it the way
I THINK you meant it, but that doesn't guarantee anything.
-- Simon is riding his bike at 12 km/hr relative to the sidewalk,
away from Keesha.
-- He throws a ball at Keesha, at 5 km/hr relative to his own face.
-- Keesha sees the ball approaching her at (12 - 5) = 7 km/hr
relative to the ground and to her.
<h2>Answer: 10.52m</h2><h2 />
First, we have to establish the <u>reference system</u>. Let's assume that the building is on the negative y-axis and that the brick was thrown at the origin (see figure attached).
According to this, the initial velocity 
has two components, because the brick was thrown at an angle 
:
(1)
(2)
(3)
(4)
As this is a projectile motion, we have two principal equations related:
<h2>
In the x-axis:
</h2>
(5)
Where:
is the distance where the brick landed
is the time in seconds
If we already know 
and 
, we have to find the time (we will need it for the following equation):
(6)
(7)
<h2>
In the y-axis:
</h2>
(8)
Where:
is the height of the building (<u>in this case it has a negative sign because of the reference system we chose)</u>
is the acceleration due gravity
Substituting the known values, including the time we found on equation (7) in equation (8), we will find the height of the building:
(9)
(10)
Multiplying by -1 each side of the equation:
>>>>This is the height of the building
Answer:
4 km/hr
Explanation:
suppose 's' is Diane's speed with no current.
't' represents time in hrs.
Using the formula:
Distance = speed 's' x time 't'
-> when she swims against the current, equation will be,
5= (s-2)t
t= 5/(s-2)
->when she was swimming with the current, equation is,
15= (s+2) t
t= 15/(s+2)
equating eq(1) and (2)
5/(s-2) = 15/(s+2)
5s + 10 = 15s - 30
40= 10s
s= 40/10
s=4
Therefore, if there were no current, her speed is 4km/hr
