A playing card (4 grams) is held against a vertical wall by a pencil (20 grams). The pencil is perpendicular to the wall and exerts a horizontal force 0.4 N. The coefficient of static friction between the wall and the card is 0.2. Assume the card is still. (We will investigate this assumption in question 12.) (Use g = 10 m/s2.)
What is the magnitude of the force of static friction on the card?