Compute the resistance of a hardened copper rod 2 meters long and 8 mm in diameter if resistivity of the material is 1.756 x 10^(-8) ohm-meters?

The resistance of the copper rod =  4.39×10⁻¹⁵ Ohms.

Explanation:

Resistance: This is the opposition to current flow in a circuit.

The S.I unit of resistance is Ohms.

R = Aσ/L Equation 1

Where σ = resistivity of the copper, R = resistance of the copper rod,  A = cross sectional area of the copper, L = length of the copper rod.

Given:

σ = 1.756×10⁻⁸ ohm-meters, L = 2 meters.

But A = πd²/4

Where d = 8 mm = (8/1000) m = 0.0008 m, π = constant = 3.143

Therefore,

A = 3.143(0.0008)²/4

A = 0.0000005 m²

Substituting these values into equation 1,

R = 5×10⁻⁷×1.756×10⁻⁸/2

R = (8.78 ×10⁻¹⁵)/2

R = 4.39×10⁻¹⁵ Ohms.

Thus the resistance of the copper rod =  4.39×10⁻¹⁵ Ohms.

force is based upon mass and acceleration.the statement is not always true.

it can be explained from newton's second law of motion.

as per newton's second law of motion the rate of change of momentum is directly proportional to the applied force and takes place along the direction of force.

mathematically it can be written as -

                                              ⇒      

here   k is the proportionality constant whose value is 1.

                                                            [a is the acceleration=dv/dt]

hence we see that force not only depends on mass and acceleration but also on velocity and rate of change of mass. force f will depend on mass and acceleration only when mass is constant.

hence the statement that force is based upon mass and acceleration is false.