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Difficulty: Very hardLevers and Fulcrums

Match each mechanical scenario to its correct lever classification and mechanical advantage (MA) property.

  • A heavy-duty pry bar where the pivot point is placed between the operator's hands and a heavy crate, significantly closer to the crate.Class 1 Lever; acts as a force multiplier (MA > 1)
  • A worker using a hand truck to transport a refrigerator, pivoting the load on the bottom wheels.Class 2 Lever; acts as a force multiplier (MA > 1)
  • A surgeon using forceps to manipulate tissue, applying inward finger pressure to the middle of the instrument.Class 3 Lever; acts as a speed and distance multiplier (MA < 1)
  • A trebuchet where a massive counterweight drops on a short arm to rapidly swing a lightweight projectile on a much longer arm.Class 1 Lever; acts as a speed and distance multiplier (MA < 1)

Answer

Pry bar matches Class 1 (MA > 1). Hand truck matches Class 2 (MA > 1). Forceps match Class 3 (MA < 1). Trebuchet matches Class 1 (MA < 1).
Each mechanism must be evaluated by locating the fulcrum, effort, and load. A pry bar and trebuchet both have the fulcrum in the middle (Class 1), but differ in their arm ratios, resulting in MA > 1 and MA < 1 respectively. A hand truck has the load in the middle (Class 2, MA > 1). Forceps have the effort in the middle (Class 3, MA < 1).

Step-by-Step Solution

1
Analyze the pry bar scenario.
Identified as a Class 1 lever with MA > 1.
The fulcrum is located between the effort (operator) and the load (crate). Because the fulcrum is placed closer to the load, the effort arm is longer than the load arm, creating a mechanical advantage greater than 1.
2
Analyze the hand truck scenario.
Identified as a Class 2 lever with MA > 1.
The wheels serve as the fulcrum at one end. The refrigerator's weight (load) acts in the middle, and the operator's hands apply effort at the opposite end. This configuration is a Class 2 lever, which inherently multiplies force (MA > 1).
3
Analyze the forceps scenario.
Identified as a Class 3 lever with MA < 1.
The joined end is the fulcrum. The surgeon applies effort to the middle of the tool, and the tissue is the load at the far end. Effort in the middle defines a Class 3 lever, which always acts to multiply distance and speed at the expense of force (MA < 1).
4
Analyze the trebuchet scenario.
Identified as a Class 1 lever with MA < 1.
The pivot is between the dropping counterweight (effort) and the projectile (load), making it a Class 1 lever. Because the effort arm is much shorter than the load arm, the mechanical advantage is less than 1, which serves to drastically increase the speed of the projectile.

Key Concept

Identifying the relative positions of the fulcrum, effort, and load to classify levers (Class 1, 2, or 3) and analyzing arm lengths to determine if the mechanism multiplies force (MA > 1) or speed (MA < 1).
Estimated Time:2m 0s
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Topics

Levers and Fulcrums

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