You haven't said how much power the stereo uses. It matters !
Whatever that number is, the maximum hours per month is
(3460) divided by (the # of watts the stereo uses when it's playing) .
Answer:

and

Explanation:
See attached figure.
E due to sphere
E due to particule
(1)
according to the law of gauss and superposition Law:
; electric field due to the small sphere with r1=R/4


then:
(2)
on the other hand, for the particule:

⇒
(3)
We replace (2) y (3) in (1):


--------------------
if R<x<2R AND 

remember that 
then:

solving:


but: R<x<2R
so : 
The correct answer is:
<span>B.) At terminal velocity there is no net force
In fact, when the parachutist reaches the terminal velocity, his velocity does not change any more. It means that the acceleration acting on the parachutist is zero, and for Newton's second law, this means the net force acting on him is zero:
</span>

<span>because the acceleration is zero: a=0.
This also means that the two relevant forces acting on the parachutist (gravity, downward, and air resistance, upward) are balanced to produce a net force equal to zero.</span>
The area of a triangle is found by multiplying the height of the triangle by the length of the base and dividing them both by 2. The length of the shorter side in the equation is useless information, so just multiply 39 by 25 and divide that by 2. A=487.5 sq ft. Also, that's a pretty big kite.
Hi there!
We can use the kinematic equation:

vf = Final velocity (? m/s)
vi = initial velocity (0 m/s, dropped from rest)
a = acceleration (due to gravity, 9.8 m/s²)
d = distance (9.8 m)
Simplify the equation to solve for vf:

Substitute in the given values:
