Bennett Mechanical Pulleys and Levers Questions and Answers 1 — Questions and Answers
Question 1: In the pulley system shown, assuming the system is frictionless, what is the minimum force (F) required to lift the 120kg weight?
- 60 kg
- 120 kg
- 30 kg
- 40 kg (Correct answer)
Correct answer: 40 kg
The mechanical advantage of a pulley system is equal to the number of rope segments supporting the load. In this diagram, there are 3 ropes directly supporting the movable pulley and the weight. Therefore, the force required is the total weight divided by the mechanical advantage (120 kg / 3 = 40 kg).
Question 2: A wheelbarrow is an example of which class of lever?
- First-Class Lever
- Second-Class Lever (Correct answer)
- Third-Class Lever
- Fourth-Class Lever
Correct answer: Second-Class Lever
A wheelbarrow is a second-class lever. In a second-class lever, the load (the contents of the wheelbarrow) is located between the fulcrum (the wheel's axle) and the effort (the force applied to the handles).
Question 3: If person X wants to balance the seesaw, in which direction should they move?
- Towards A (Correct answer)
- Towards B
- They should stay in the same position
- It is impossible to balance
Correct answer: Towards A
To balance the seesaw, the torque on both sides of the fulcrum must be equal. Torque is calculated as Force x Distance from the fulcrum. Since the weight on the right side is heavier, person X, who is lighter, must increase their distance from the fulcrum to increase their torque. Moving towards A increases this distance.
Question 4: Which of the following scenarios provides the greatest mechanical advantage?
- A single fixed pulley changing the direction of pull.
- A single movable pulley attached to the load. (Correct answer)
- Using a pair of tweezers to pick up a small object.
- A fishing rod casting a line.
Correct answer: A single movable pulley attached to the load.
A single movable pulley provides a mechanical advantage of 2, meaning it halves the effort needed to lift a load. A single fixed pulley only changes the direction of force and has a mechanical advantage of 1. Tweezers and fishing rods are third-class levers, where the effort is between the fulcrum and the load, resulting in a mechanical advantage of less than 1.
Question 5: To lift a 200 lb engine out of a car, a mechanic uses a pulley system. If the mechanic can only pull with 50 lbs of force, what is the minimum mechanical advantage the pulley system must have (ignoring friction)?
- 2
- 3
- 4 (Correct answer)
- 5
Correct answer: 4
Mechanical Advantage (MA) is the ratio of the load force to the effort force (MA = Load / Effort). In this case, the load is 200 lbs and the effort is 50 lbs. Therefore, the required mechanical advantage is 200 / 50 = 4.
Question 6: Using a crowbar to pry open a crate is an application of a first-class lever. Where is the fulcrum located in this action?
- At the handle end where force is applied.
- At the point where the crowbar lifts the crate lid.
- At the point where the crowbar rests on the edge of the crate. (Correct answer)
- In the middle of the crowbar's length.
Correct answer: At the point where the crowbar rests on the edge of the crate.
In a first-class lever, the fulcrum is located between the effort and the load. When using a crowbar to open a crate, the effort is applied to the handle, the load is the resistance from the crate lid, and the fulcrum is the point where the crowbar pivots on the edge of the crate.
Bennett Mechanical Pulleys and Levers Questions and Answers 1
In the pulley system shown, assuming the system is frictionless, what is the minimum force (F) required to lift the 120kg weight?