About Mechanical Comprehension (Aptitude)
Mechanical Comprehension or mechanical aptitude questions are found on the ASVAB, Canadian Firefighter and Elevator Industry Aptitude tests. Other occupations are, Automotive and Aircraft Mechanics, Engineers, Installation and Maintenance Repair people, Industrial and Technical (Non-Retail) Sales Representatives, and Skilled Tradespeople such as Electricians, Welders, and Carpenters Transportation Trades and Equipment Operators such as Truck drivers and Heavy Equipment Operators.
- Belt Pulley
- Closed Circuit
- Electrical Circuit
- Electrical Load
- Electrical Path
- Electrical Switch
- Horseshoe Magnet
- Knife Switch
- Open Circuit
- Parallel circuit
- Pivot point
- Positive and Negative poles
- Series Circuit
- Short Circuit
- Toggle Switch
- Weight time Distance
Practice Test Questions
1. What is mechanical advantage?
a. The ratio of energy input to energy output, typically where the input is less than the output.
b. The ratio of energy input to energy output, typically where the input is greater than the output.
c. The ratio of energy resistance to energy output, typically where the resistance is less than the output.
d. None of the above.
2. What is the ratio of mechanical advantage of a simple pulley?
3. If a 100-pound object is sitting on a 10-square-inch plate, what is the PSI?
4. Consider moving an object with a level and a fulcrum. What is the relationship between the distance from the fulcrum and the speed the object will move?
a. The farther away from the fulcrum, the faster the object will move.
b. The closer to the fulcrum, the faster an object will move.
c. An object will move the fastest when directly above the fulcrum.
d. None of the above.
5. Which of the following are examples of a wedge?
6. Which of the following illustrates the principal of the lever?
a. The greater the distance over which the force is applied, the greater the force required (to lift the load).
b. The greater the distance over which the force is applied, the smaller the force required (to lift the load).
c. The smaller the distance over which the force is applied, the smaller the force required (to lift the load).
d. None of the above.
7. Which of the following is true of the relationship between screws and threads?
a. The larger the distance between threads, the easier to turn.
b. The smaller the distance between threads, the easier to turn.
c. The smaller the distance between threads, the more difficult to turn.
d. None of the above
8. Which of the following is an example of torque?
a. The wheel of a pulley turning
b. A piston moving
c. A horse pulling a load
d. A tow truck pulling a vehicle
9. Consider the pulley arrangement above. If the weight, W, is 50 pounds, how much force is required to lift it?
a. 10 pounds
b. 20 pounds
c. 25 pounds
d. 50 pounds
10. Consider a gear train with 3 gears, from left to right, A with 20 teeth, gear B with 60 teeth, and gear C with 10 teeth. Gear A turns clockwise at 60 rpm. What direction and speed in rpm does Gear C turn?
a. 120 rpm, clockwise
b. 100 rpm clockwise
c. 120 rpm counter clockwise
d. 140 rpm counter clockwise
The ratio of energy input to energy output, typically where the input is less than the output. Mechanical advantage is a measure of the force amplification achieved by using a tool, mechanical device or machine system. Ideally, the device preserves the input power and simply trades off forces against movement to obtain a desired amplification in the output force. The model for this is the law of the lever. Machine components designed to manage forces and movement in this way are called mechanisms.
The ratio of mechanical advantage of a simple pulley is 1:1.
Calculate the PSI by taking the weight divided by the size of the object the weight is bearing on. 100/10 = 10 PSI.
The farther away from the fulcrum, the faster the object will move.
Examples of wedges include the cutting edge of scissors, knives, screwdrivers, doorstops, nails axes and chisels.
The greater the distance over which the force is applied, the smaller the force required (to lift the load).
The smaller the distance between threads, the easier to turn.
The wheel of a pulley turning is an example of torque. Torque, moment or moment of force, is the tendency of a force to rotate an object about an axis, fulcrum, or pivot. Just as a force is a push or a pull, a torque can be thought of as a twist to an object.
Since the weight is only attached to one pulley, the force required will be 50/2 = 25 pounds.
First calculate the speed of gear B. The gear ratio is 60:20 or 3:1. If gear A is turning at 60 rpm, then gear B will turn at 30/3 = 20 rpm.
Next calculate B and C. Gear C is smaller, so it will turn faster. The gear ratio is 60:10 or 6:1, and since gear B turns at 20 rpm, gear C will turn at 20 X 6 = 120 rpm.
Next calculate the direction. Gear A is turning clockwise, so Gear B is turning counter clockwise, so Gear C must be turning clockwise.