The temperature T in a metal ball is inversely proportional to the distance from the center of the ball, which we take to be the origin. The temperature at the point (1, 2, 2) is 160°. (a) Find the rate of change of T at (1, 2, 2) in the direction toward the point (4, 1, 3). Incorrect: Your answer is incorrect. (b) Show that at any point in the ball the direction of greatest increase in temperature is given by a vector that

The answers to the questions are as follows;

(a) The rate of change of T at (1, 2, 2) in the direction toward the point (4, 1, 3) is  

(b) The direction of the gradient is in the direction of greatest increase and it is towards the origin.

Explanation:

To solve the question, we note that the shape of the ball is that of a sphere.

Therefore the distance of a point from the center is given by

f(x, y, z)  =

The temperature T in a metal ball is inversely proportional to the distance from the center of the ball

Therefore T ∝ or T =

Where

C = Constant of proportionality

x, y, and z are the x, y and z coordinates values

To find C, we note that at point (1, 2, 2), T = 160 °C.

Therefore 160 °C = = =

Therefore C = 160 × 3 = 480 °C·(Unit length)

We therefore have the general equation as

T =

The vector from points  (1, 2, 2) to point (4, 1, 3) is given by

1·i + 2·j +2·k - (4·i + 1·j +3·k) = -3·i + j -k

From which we find the unit vector given by

u =  

From which we have the gradient equal to

∇T(x, y, z) = -480×(x²+y²+z²) in (x, y, z)

This gives D = ∇T·u

                       = -480×(x²+y²+z²) in (x, y, z)·

That is

(x²+y²+z²) (-3·x + y - z)

From where DTat point (1, 2, 2) is  =  

(b) The direction of greatest increase in temperature is in the direction of the gradient and the direction of the gradient is opposite to the direction of {x, y, z}, which is away from the origin.

Hence the direction of the greatest increase in temperature is towards the origin.

air exerts forces on falling objects near earth’s surface.

explanation:

the term 'free falls' refer to object that are falling towards the earth, in a situation in which gravity is the only force acting on the object.

for an object in free fall, the acceleration is constant (g, the gravitational acceleration), and so the velocity of the object constantly increases.

for objects near earth's surface, there is always another force acting on the object: the resistance due to the air. this force is opposed to the direction of fall of the object, and it is proportional to the velocity of the object, so as the object falls down, this force increases up to a point when it balances the force of gravity, and the object continues its motion at constant velocity (called terminal velocity). since in this case gravity is not the only force acting on the object, we are not in a situation of free fall.