Just Physics

← Unit 2 Handouts

Topic 2.2: Practice Sheet — Forces and Free-Body Diagrams

Name: _______________________________ Date: _______________ Period: ______

Directions: Show your work for every problem — a correct answer with no work shown earns partial credit at best. Circle or box your final answer. For "is this claim valid" questions, a full sentence explanation is required, not just yes/no.

Warm-Up Level (straightforward, one-step)

  1. Two forces act on an object: 6 N to the right and 8 N straight up. Find the magnitude of the net force.
  2. Draw a simple FBD (dot + labeled arrows only, no numbers needed) for a book resting motionless on a table.

Standard Level (multi-step, matches typical AP Classroom depth)

  1. Two forces act on an object: 5 N to the right and 12 N straight up. Find the magnitude and direction (angle above horizontal) of the net force.
  2. A block sits on a frictionless incline at 25° to the horizontal. Write the expression (do not calculate a number) for the component of gravity acting along the incline's surface.
  3. A classmate says: "Tension in a rope holding up a motionless sign and the sign's weight are equal and opposite, so they must be a Newton's-third-law pair." Is this reasoning valid? Explain why or why not.

AP-Level (multi-part: calculate + justify/represent/predict-a-change)

  1. A crate sits motionless on a ramp inclined at 20°, held in place by friction only (no rope). a) Sketch the FBD, labeling all forces (gravity, normal, friction). b) Write the expression for the component of gravity along the ramp's surface, and explain in words why the friction force must have the same magnitude as that component.
  2. A sign hangs motionless from a single vertical rope. Partway through the day, the rope is cut. a) Before the rope is cut, is the net force on the sign zero? Justify your answer using the sign's FBD. b) The instant after the rope is cut, is the net force on the sign zero? Explain what changes on the FBD and why.

Progress Check Style (evaluate the method — AP Classroom format)

  1. Two forces act on an object on a grid: 9 N to the right and 12 N straight up. Which of the following is the magnitude of the net force? (A) 21 N (B) 15 N (C) 3 N (D) 10.5 N

Keep this sheet — it's part of your semester study materials, same as your Concept Sheets.