A 20 kg metal block is placed on a horizontal surface. The block just

1.	A 20 kg metal block is placed on a horizontal surface. The block just begins to slide when horizontal force of 100 N is applied to it.Calculate the coefficient of static friction. If coefficient of kinetic friction is 0.4, then find minimum force to maintain its uniform motion.
Answer» Given: m = 20 kg, F_L = 100 N, μ_k = 0.4 To find: i. Coefficient of static friction (μ_S) ii. Minimum force required (F_k) Formulae: i. μs = \(\frac{F_L}{N}=\frac{F_L}{mg}\) ii. μS = \(\frac{F_K}{N}\) Calculation: From formula (i), μ_s = \(\frac{100}{20\times9.8}\) = 0.5102 From formula (ii), F_k = μ_kN = μ_k × mg = 0.4 × 20 × 9.8 ∴ F_k = 78.4 N 1. The coefficient of static friction is 0.5102. 2. The minimum force required is 78.4 N.

A 20 kg metal block is placed on a horizontal surface. The block just begins to slide when horizontal force of 100 N is applied to it.Calculate the coefficient of static friction. If coefficient of kinetic friction is 0.4, then find minimum force to maintain its uniform motion.

Answer»

Given: m = 20 kg, F_L = 100 N, μ_k = 0.4

To find:

i. Coefficient of static friction (μ_S)

ii. Minimum force required (F_k)

Formulae:

i. μs = \(\frac{F_L}{N}=\frac{F_L}{mg}\)

ii. μS = \(\frac{F_K}{N}\)

Calculation:

From formula (i),

μ_s = \(\frac{100}{20\times9.8}\) = 0.5102

From formula (ii),

F_k = μ_kN = μ_k × mg = 0.4 × 20 × 9.8

∴ F_k = 78.4 N

1. The coefficient of static friction is 0.5102.

2. The minimum force required is 78.4 N.