Answer:
I₂ = 8 mG
Explanation:
The intensity of a beam is
I = P / A
Where P is the emitted power which is 3) 3
Let's use index 1 for the initial position of r₁ = 6 ft and 2 for the second position r₂ = 3 ft
I₁ A₁ = I₂ A₂
I₂ = I₁ A₁ / A₂
The area of the beam if we assume that it is distributed either in the form of a sphere is
A₁ = 4π r²
We substitute
I₂ = I₁ (r₁ / r₂)²
I₂ = 2 (6/3)²
I₂ = 2 4
I₂ = 8 mG
The crate is in equilibrium. Newton's second law gives
∑ <em>F</em> (vertical) = <em>n</em> - <em>mg</em> = 0
∑ <em>F</em> (horizontal) = <em>p</em> - <em>f</em> = 0
where
• <em>n</em> = magnitude of the normal force
• <em>mg</em> = weight of the crate
• <em>p</em> = mag. of push exerted by movers
• <em>f</em> = mag. of kinetic friciton, with <em>f</em> = 0.60<em>n</em>
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It follows that
<em>p</em> = <em>f</em> = 0.60<em>mg</em> = 0.60 (43.0 kg) <em>g</em> = 252.84 N
so that the movers perform
<em>W</em> = <em>p</em> (10.4 m) ≈ 2600 J
of work on the crate. (The <em>total</em> work done on the crate, on the other hand, is zero because the net force on the crate is zero.)
Answer:
121 Joules
6.16717 m
Explanation:
m = Mass of the rocket = 2 kg
k = Spring constant = 800 N/m
x = Compression of spring = 0.55 m
Here, the kinetic energy of the spring and rocket will balance each other

The initial velocity of the rocket is 11 m/s = u.
v = Final velocity
s = Displacement
a = Acceleration due to gravity = 9.81 m/s² = g

The maximum height of the rocket will be 6.16717 m
Potential energy is given by

The potential energy of the rocket at the maximum height will be 121 Joules
To calculate the length of the wire, we use formulas,
(A)
(B)
Here, R is the resistance of the wire, I is the current flows through wire and V is potential difference. A is cross sectional area of wire and
is the density of copper wire and is value,
.
Given 
Substituting the values of I and V in equation (A ) we get,

Now from equation (B),

Therefore,

Thus the length of the copper wire is 177.9 m.