newton's law of motion

Question

A person is sliding a 12.0 kg block across ice that has a coefficient of kinetic friction of 0.100. How much force does the person need to apply to keep the block moving at a constant rate?

Answer 1

By Newton’s Second Law the sum of forces equals the acceleration, since velocity is constant the acceleration is zero so the force applied by the person is equal to the force of friction, µmg. So force applied equals

.1(12)(9.8) = 11.8 N

Answer 2

F = μmg = 0.1·12kg·9.8m/s² = 11.76 N (F must compensate friction)