Darker is warmer C. Black objects.
Answer:
g= 9.81m/s..................
Answer:
Rectangular path
Solution:
As per the question:
Length, a = 4 km
Height, h = 2 km
In order to minimize the cost let us denote the side of the square bottom be 'a'
Thus the area of the bottom of the square, A = 
Let the height of the bin be 'h'
Therefore the total area, 
The cost is:
C = 2sh
Volume of the box, V =
(1)
Total cost,
(2)
From eqn (1):

Using the above value in eqn (1):


Differentiating the above eqn w.r.t 'a':

For the required solution equating the above eqn to zero:


a = 4
Also

The path in order to minimize the cost must be a rectangle.
Answer:
The two objects will collide with the same position vector for all three components at exactly t = 4 s
Explanation:
For two particles starting out at the same time to collide, their position Vector's at the time of collision must be exactly the same.
So, at the collision point, position vector of object 1 is equated to that of object 2.
r₁ = (t², 13t-36, t²)
r₂ = (7t-12, t², 5t-4)
At he point of collision
t² = 7t - 12
t² - 7t + 12 = 0
t² - 4t - 3t + 12 = 0
t(t - 4) - 3(t - 4) = 0
t = 3s or t = 4s
13t - 36 = t²
t² - 13t + 36 = 0
t² - 4t - 9t + 36 = 0
t(t - 4) - 9(t - 4) = 0
t = 9s or 4s
t² = 5t - 4
t² - 5t + 4 = 0
t² - 4t - t + 4 = 0
t(t - 4) - 1(t - 4) = 0
t = 1s or t = 4s
The three components intersect at other times, but at t = 4s, they all intersect at the same time! Meaning that, at this point the two objects are at the same place with the same position vector at that time.