The resistance of a coil is 4.2 ohm at 100 degree centigrade and the temperature coefficient of resistance of its material is 0.004 per degree centigrade. Its resistance at 0 degree centigrade

3 ohms

Explanation:

Applying,

R₁₀₀ = R₀(1+αΔT) Equation 1

Where α = coefficient of resistance, ΔT = change in temperature, R₁₀₀ and R₀ = Resistance at 100°C and 0°C respectively

make R' the subject of the equation

R₀ = R₁₀₀/(1+αΔT) Equation 2

From the question,

Given:  R₁₀₀ = 4.2 ohm, α = 0.004 per degree, ΔT = 100-0 = 100°C

Substitute these values into equation 2

R₀ = 4.2(1+0.004×100)

R₀ = 4.2/1.4

R₀ = 3 ohms

the answer would be c

b. lifting dumbbell weight at 20-degree angle from the body after a 45-degree angle