Bennett Mechanical Pulleys and Levers 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?

Accepted Answer

40 kg

Answer

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?

Accepted Answer

Second-Class Lever

Answer

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?

Accepted Answer

Towards A

Answer

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?

Accepted Answer

A single movable pulley attached to the load.

Answer

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)?

Accepted Answer

4

Answer

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.

Bennett Mechanical Test Practice Test

Bennett Mechanical Test Practice Test

Bennett Mechanical Pulleys and Levers Questions and Answers