When an object rests on a surface, there is always a force perpendicular to the surface; we call this the normal force, denoted by n? . The two questions to the right will explore the normal force.

Part A. A man attempts to pick up his suitcase of weight ws by pulling straight up on the handle. However, he is unable to lift the suitcase from the floor. Which statement about the magnitude of the normal force n acting on the suitcase is true during the time that the man pulls upward on the suitcase?

The magnitude of the normal force is equal to the magnitude of the weight of the suitcase.
The magnitude of the normal force is equal to the magnitude of the weight of the suitcase minus the magnitude of the force of the pull.
The magnitude of the normal force is equal to the sum of the magnitude of the force of the pull and the magnitude of the suitcase's weight.
The magnitude of the normal force is greater than the magnitude of the weight of the suitcase.

Part B. Now assume that the man of weight wm is tired and decides to sit on his suitcase. Which statement about the magnitude of the normal force n acting on the suitcase is true during the time that the man is sitting on the suitcase?

The magnitude of the normal force is equal to the magnitude of the suitcase's weight.
The magnitude of the normal force is equal to the magnitude of the suitcase's weight minus the magnitude of the man's weight.
The magnitude of the normal force is equal to the sum of the magnitude of the man's weight and the magnitude of the suitcase's weight.
The magnitude of the normal force is less than the magnitude of the suitcase's weight.