ASVAB Mechanical Comprehension Practice Test 507953 Results

	Your Results	Global Average
Questions	5	5
Correct	0	2.99
Score	0%	60%

Review

What is work?

60% Answer Correctly

	Force per unit time
	The potential for exertion
	Force per unit distance
	The movement of an object by a force

Solution

Work is accomplished when force is applied to an object: W = Fd where F is force in newtons (N) and d is distance in meters (m). Thus, the more force that must be applied to move an object, the more work is done and the farther an object is moved by exerting force, the more work is done. By definition, work is the displacement of an object resulting from applied force.

The steering wheel of a car is an example of which type of simple machine?

89% Answer Correctly

	block and tackle
	first-class lever
	fixed pulley
	wheel and axle

Solution

A wheel and axle uses two different diameter wheels mounted to a connecting axle. Force is applied to the larger wheel and large movements of this wheel result in small movements in the smaller wheel. Because a larger movement distance is being translated to a smaller distance, force is increased with a mechanical advantage equal to the ratio of the diameters of the wheels. An example of a wheel and axle is the steering wheel of a car.

Which of the following is the formula for torque?

61% Answer Correctly

	τ = F/r
	τ = rF
	τ = F/r²
	τ = r/F

Solution

Torque measures force applied during rotation: τ = rF. Torque (τ, the Greek letter tau) = the radius of the lever arm (r) multiplied by the force (F) applied. Radius is measured from the center of rotation or fulcrum to the point at which the perpendicular force is being applied. The resulting unit for torque is newton-meter (N-m) or foot-pound (ft-lb).

4 What is the power output of a 1 hp engine that's 65% efficient?

39% Answer Correctly

	715 \( \frac{ft⋅lb}{s} \)
	357.5 \( \frac{ft⋅lb}{s} \)
	89.4 \( \frac{ft⋅lb}{s} \)
	119.2 \( \frac{ft⋅lb}{s} \)

Solution

\( Efficiency = \frac{Power_{out}}{Power_{in}} \times 100 \)
Solving for power out: \( P_{o} = \frac{E \times P_{i}}{100} \)
Knowing that 1 hp = 550 \( \frac{ft⋅lb}{s} \), P_i becomes 1 hp x 550 \( \frac{ft⋅lb}{s} \) = 550 \( \frac{ft⋅lb}{s} \)
\( P_{o} = \frac{E \times P_{i}}{100} = \frac{65 \times 550 \frac{ft⋅lb}{s}}{100} \) \( = \frac{35750 \frac{ft⋅lb}{s}}{100} \) = 357.5 \( \frac{ft⋅lb}{s} \)

Which of the following statements about this pulley configuration is false?

48% Answer Correctly

	Changes the direction of and multiplies the effort force
	Only multiplies the effort force
	This is a block and tackle pulley configuration
	Mechanical advantage is the number of ropes that support the resistance

Solution

A block and tackle is a combination of one or more fixed pulleys and one or more movable pulleys where the fixed pulleys change the direction of the effort force and the movable pulleys multiply it. The mechanical advantage is equal to the number of times the effort force changes direction and can be increased by adding more pulley wheels to the system. An easy way to find the mechanical advantage of a block and tackle pulley system is to count the number of ropes that support the resistance.