ASVAB Mechanical Comprehension Practice Test 415252 Results

	Your Results	Global Average
Questions	5	5
Correct	0	3.01
Score	0%	60%

Review

1 If the radius of the axle is 3 and the radius of the wheel is 8, what is the mechanical advantage of this wheel and axle configuration?

52% Answer Correctly

	0.38
	2.67
	3
	-5

Solution

The mechanical advantage of a wheel and axle is the input radius divided by the output radius:

MA = \( \frac{r_i}{r_o} \)

In this case, the input radius (where the effort force is being applied) is 8 and the output radius (where the resistance is being applied) is 3 for a mechanical advantage of \( \frac{8}{3} \) = 2.67

2 If input effort is 800 ft⋅lb, what output effort will be produced by a machine with a mechanical advantage of 6?

79% Answer Correctly

	133ft⋅lb
	19200ft⋅lb
	1200ft⋅lb
	4800 ft⋅lb

Solution

Mechanical advantage is the ratio of output force to input force and tells us by how many times a machine multiplies input effort. So, a machine with a mechanical advantage of 6 will multiply an input effort of 800 ft⋅lb by 6 to produce an output effort of 4800 ft⋅lb.

Which class of lever offers no mechanical advantage?

45% Answer Correctly

	none of these, all levers offer mechanical advantage
	third
	first
	second

Solution

A third-class lever is used to increase distance traveled by an object in the same direction as the force applied. The fulcrum is at one end of the lever, the object at the other, and the force is applied between them. This lever does not impart a mechanical advantage as the effort force must be greater than the load but does impart extra speed to the load. Examples of third-class levers are shovels and tweezers.

4 If a 30 lbs. weight is placed 5 ft. from the fulcrum at the blue arrow and the green box is 2 ft. from the fulcrum, how much would the green box have to weigh to balance the lever?

61% Answer Correctly

	300 lbs.
	25 lbs.
	18.75 lbs.
	75 lbs.

Solution

To balance this lever the torques on each side of the fulcrum must be equal. Torque is weight x distance from the fulcrum so the equation for equilibrium is:

R_ad_a = R_bd_b

where a represents the left side of the fulcrum and b the right, R is resistance (weight) and d is the distance from the fulcrum.

Solving for R_a, our missing value, and plugging in our variables yields:

R_a = \( \frac{R_bd_b}{d_a} \) = \( \frac{30 lbs. \times 5 ft.}{2 ft.} \) = \( \frac{150 ft⋅lb}{2 ft.} \) = 75 lbs.

Sam can do 50 ft. lb. of work in 2 minutes and 5 seconds. What would Sam have to do to increase his power output?

64% Answer Correctly

	do the work in 2 minutes
	do the work in 3 minutes
	do 100 ft. lb. of work in 4 minutes 12 seconds
	do 25 ft. lb. of work in 2 minutes 5 seconds

Solution

Power is the rate of doing work or \(\frac{W}{t}\). To increase power, increase the work being done in the same amount of time or do the same amount of work in less time.