Question

In each of the following cases identify all objects in the surroundings that exert forces on the system, and draw a free-body diagram for the system. Assume that air resistance is negligible. (a) You hit a baseball with a bat. Choose the baseball as the system, and consider the instant of contact with the bat. (b) You are playing with a yo-yo. Choose the yo-yo as the system. As the yo-yo moves downward, you pull up on the string.

Short answer

(a) The free body diagram of the baseball as a system has been drawn below.

(b) The free body diagram of the yo-yo as a system has been drawn below.

Step-by-step solution

Identification of the given data 

The given data is listed below,

The air resistance is negligible.

Significance of Newton’s first law for the objects

This law states that a body will continue to move in a straight line in a uniform motion if no external force acts on that body.

Newton’s first law helps in identifying the forces in the free body diagram of the baseball-bat system and the yo-yo system.

Determination of the free body diagram when baseball is considered a system

(a)

The forces that will act on the baseball if it is considered as the system are force due to the hitting of the bat and the force due to gravity.

The free-body diagram of the baseball and the bat is drawn below,

Here, $F_{bat}$is the force exerted by the bat on the baseball and $F_g$is the force due to the gravity.

(b) Determination of the free body diagram when the yo-yo is considered a system

The forces that will act on the baseball if it is considered as the system are force applied for pulling the yo-yo and the force due to gravity.

The free-body diagram of the yo-yo as a system has been drawn below-

Here, $F_s$is the force needed to pull up the yo-yo and $F_g$is force acting downwards due to the acceleration due to gravity.