Two 4 gram playing cards are balanced against each other, as shown. You find that you can incline the cards 22 degrees from the vertical before they slip on the table and fall flat.
What is the coefficient of friction between the table and cards?
If the angle from the vertical is only 15 degrees instead, what is the maximum vertical load (downward force exerted on the cards) that they can take without slipping? Assume that the force is applied at the tip, with half of it held by each card.