Question

A 10N force is applied to a 5kg object resulting in an acceleration of 0.5m/s2. What is the force of friction acting on that object?

Answer 1

Let's apply Newton's Second Law of Motion:

$$F_{appl}-F_{fr}=ma,$$ $$F_{fr}=F_{appl}-ma,$$ $$F_{fr}=10\ N-5\ kg\times0.5\ \dfrac{m}{s^2}=7.5\ N.$$