Mechanical Comprehension Flashcards

In the gear system shown, Gear X has 10 teeth and rotates clockwise. Gear Y has 20 teeth, and Gear Z has 10 teeth. Which of the following statements is true?

Answer: Gear Z rotates clockwise at the same speed as Gear X.

When gears are meshed, they rotate in opposite directions. Gear X (clockwise) turns Gear Y (counter-clockwise). Gear Y (counter-clockwise) then turns Gear Z (clockwise). Because Gear X and Gear Z have the same number of teeth (10), they will rotate at the same speed, but Gear Y, which has more teeth, will rotate slower. The idler gear (Y) only serves to change the direction of rotation back to the original.

A bimetallic strip is made of copper and steel bonded together. The coefficient of thermal expansion for copper is higher than that of steel. If the strip is heated, what will happen?

Answer: The strip will bend with the copper on the outside of the curve.

When heated, both metals expand, but copper expands more than steel due to its higher coefficient of thermal expansion. To accommodate this differential expansion, the bonded strip must bend. The material that expands more (copper) will form the longer, outer side of the curve.

In the pulley system shown, a person is lifting a 100 kg weight. Ignoring the weight of the rope and pulleys and any friction, what is the minimum force required to lift the weight?

Answer: 25 kg

The mechanical advantage of a pulley system is equal to the number of rope segments directly supporting the movable load. In this system, the 100 kg weight is supported by 4 rope segments. Therefore, the required force is the total weight divided by the mechanical advantage (100 kg / 4), which equals 25 kg.

Which of the following designs for a cargo truck is the most stable and least likely to tip over on a sharp turn?

Answer: A truck with a low center of gravity and a wide wheelbase.

An object's stability is increased by having a low center of gravity and a wide base of support. A low center of gravity makes the object less likely to be tipped, and a wide wheelbase provides a larger base of support, meaning the object can be tilted at a greater angle before its center of gravity moves outside the base.

A hydraulic lift is used to raise a car. A force of 100 N is applied to a small piston with an area of 5 cm². If the large piston has an area of 500 cm², what is the maximum lifting force that can be generated?

Answer: 10,000 N

This scenario applies Pascal's Principle, which states that pressure applied to an enclosed fluid is transmitted equally throughout the fluid (Pressure = Force / Area). First, calculate the pressure from the small piston: P = 100 N / 5 cm² = 20 N/cm². This pressure is transmitted to the large piston. The lifting force is this pressure multiplied by the area of the large piston: Force = 20 N/cm² * 500 cm² = 10,000 N.

If a person uses a 2-meter long crowbar as a first-class lever to lift a heavy rock, where should the fulcrum be placed to require the least amount of effort from the person?

Answer: As close to the rock as possible.

In a first-class lever, the effort required decreases as the distance from the fulcrum to the point where effort is applied (the effort arm) increases. To maximize the effort arm's length for a given lever length, the fulcrum must be placed as close as possible to the load (the rock). This provides the greatest mechanical advantage.