Bennett Mechanical Force and Torque Questions and Answers

Question 1

Two people are carrying a heavy log. If the log has a uniform weight and they are holding it at the ends, but one person's end is propped on their shoulder (higher up) while the other person holds it at waist level (lower down), who is supporting more of the log's weight?

Accepted Answer

The person holding the log lower.

Answer

Gravity acts vertically downwards. By holding the log at an angle, the lower person supports a greater component of the vertical force (weight) than the person holding it higher. The distribution of force is no longer equal as it would be on a horizontal plane.

Question 2

To balance the lever shown, where should a 20 lb weight be placed on the right side? (The lever is marked in equal distance units from the fulcrum).

Accepted Answer

At mark 5

Answer

The principle of torque states that for a lever to be in balance, the torque on both sides of the fulcrum must be equal (Torque = Force x Distance). The left side has a torque of 10 lbs * 10 units = 100 lb-units. To balance this with a 20 lb weight, the distance must be 100 lb-units / 20 lbs = 5 units. Therefore, the weight must be placed at mark 5.

Question 3

Which of the following actions generates the most torque to loosen a tight bolt with a wrench?

Accepted Answer

Applying force at the very end of the wrench handle.

Answer

Torque is the product of the force applied and the distance from the point of rotation (the bolt). To maximize torque with a given force, you must maximize the distance from the fulcrum. Applying force at the very end of the handle provides the longest lever arm, thus generating the most torque.

Question 4

A pulley system is used to lift a 100 kg crate. System A has one fixed pulley. System B has one fixed and one movable pulley. Which statement is true regarding the force required to lift the crate?

Accepted Answer

System B requires less force.

Answer

A single fixed pulley only changes the direction of the force and has a mechanical advantage of 1. A system with one fixed and one movable pulley has a mechanical advantage of 2, meaning it effectively halves the force required to lift the weight. Therefore, System B requires less force.

Question 5

If a force of 30 Newtons is applied to a box, but the box does not move, what is the force of static friction?

Accepted Answer

Exactly 30 Newtons.

Answer

According to Newton's First Law, an object at rest stays at rest unless acted upon by a net force. Since the box is not moving, the net force on it is zero. This means the force of static friction is equal in magnitude and opposite in direction to the applied force. Therefore, the static friction is exactly 30 Newtons.

Bennett Mechanical Test Practice Test

Bennett Mechanical Test Practice Test

Bennett Mechanical Force and Torque Questions and Answers