Question

a hockey puck moves across an ice rink at a constant speed in a straight line. assume the friction is small enough to be ignored. select an fbd that correctly depicts the forces acting on the puck.

Explanation:

Step1: Analyze Motion State

The hockey puck moves at constant speed in a straight line, so net force is zero (Newton's 1st Law).

Step2: Identify Forces

Vertical forces: Normal force ($F_N$) upward, gravitational force ($F_G$) downward (balanced). Horizontal: No friction (given) and no applied force (since moving at constant speed, no net horizontal force).

Step3: Evaluate Diagrams

• First diagram: Only $F_N$, missing $F_G$ (unbalanced vertical).
• Second diagram: $F_N$ upward, $F_G$ downward (balanced vertical), no horizontal forces (consistent with zero net force).
• Third diagram: Has $F_{motion}$ (unnecessary, no applied force; also $F_N$, $F_G$, but extra horizontal force makes net force non - zero).

Answer:

The middle diagram (with $F_N$ upward and $F_G$ downward, acting on the same point)