1 . A Wooden box item sits on a horizontal wooden board. The coefficient of static friction between the box and the board is 0.5. You grab one end of the board and lift it up, keeping the other end of the board on the ground. What is the angle between the board and the horizontal direction when the box begins to slide down the board?
2. A truck is initially traveling due north at 23 m/s.
(a) Find the velocity of the car after 4 s if its acceleration is 2m/s^2 due north.
(b) Find the velocity of the car after 4 s if its acceleration is instead 2m/s^2 due south.