The half-life equation
in which <em>n </em>is equal to the number of half-lives that have passed can be altered to solve for <em>n.</em>
<em>
</em>
<em>
</em>
Then, the number of half-lives that passed can be multiplied by the length of a half-life to find the total time.
<em>2 * 5700 = </em>11400 yr
Answer:

Explanation:
Given:
<u>the thermal resistance in the form of </u>


where:
are the thickness of the respective bricks
are the respective coefficient of conductivity
temperature inside the house, 
temperature outside the house, 
area of the wall, 
Since the bricks and insulation are used to construct a wall then they must be used in series for better shielding.
<u>Using Fourier's law:</u>


in series the resistances get add up



1000 kcal because you only get 10% of the energy of the thing you eat
Answer:
you must throw 3 snowballs
Explanation:
We can solve this exercise using the concepts of conservation of the moment, let's define the system as formed by the refrigerator and all the snowballs. Let's write the moment
Initial. Before bumping that refrigerator
p₀ = n m v₀
Where n is the snowball number
Final. When the refrigerator moves
pf = (n m + M) v
The moment is preserved because the forces during the crash are internal
n m v₀ = (n m + M) v
n m (v₀ - v) = M v
n = M/m v/(vo-v)
Let's look for the initial velocity of the balls, suppose the person throws them with the maximum force if it slides in the snow (F = 100N), let's use the second law and Newton
F = m a
a = F / m
The distance the ball travels from zero speed to maximum speed is the extension of the arm (x = 1 m), let's look kinematically for the speed of the balls when leaving the arm
v₁² = v₀² + 2 a x
v₁² = 0+ 2 (100/1) 1
v₁ = 14.14 m / s
This is the initial speed for the crash
v₀ = v = 14.14 m / s
Let's calculate
n = M/m v/ (v₀-v)
n = 10/1 3 / (14.14 -3)
n = 2.7 balls
you must throw 3 snowballs
<em>Answer</em>
Force = 170 N
<em>Explanation</em>
First find the distance (d) travelled by the bulldozer.
Sin 35 = 15/d
d = 15/(sin 35)
= 26.15m
Now;
work done = force × distance.
4500 J = force × 26.15
dividing both sides by 26.15,
Force = 4500/26.15
= 172.07 N
Answer to two significant figures = 170 N