ASVAB Mechanical Comprehension Practice Test 771492 Results

	Your Results	Global Average
Questions	5	5
Correct	0	3.12
Score	0%	62%

Review

If the handles of a wheelbarrow are 3 ft. from the wheel axle, what force must you exert to lift the handles if it's carrying a 270 lb. load concentrated at a point 0.5 ft. from the axle?

56% Answer Correctly

	810 lbs
	90 lbs
	45 lbs
	0.83 lbs

Solution

This problem describes a second-class lever and, for a second class lever, the effort force multiplied by the effort distance equals the resistance force multipied by the resistance distance: F_ed_e = F_rd_r. Plugging in the variables from this problem yields:

F_e x 3 ft. = 270 lbs x 0.5 ft
F_e = 135 ft-lb. / 3 ft
F_e= 45 lbs

2 If the radius of the axle is 7 and the radius of the wheel is 12, what is the mechanical advantage of this wheel and axle configuration?

52% Answer Correctly

	5
	12
	1.71
	7

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 12 and the output radius (where the resistance is being applied) is 7 for a mechanical advantage of \( \frac{12}{7} \) = 1.71

Which of the following is not true of a first-class lever?

51% Answer Correctly

	increases distance
	changes the direction of force
	increases force
	decreases distance

Solution

A first-class lever is used to increase force or distance while changing the direction of the force. The lever pivots on a fulcrum and, when a force is applied to the lever at one side of the fulcrum, the other end moves in the opposite direction. The position of the fulcrum also defines the mechanical advantage of the lever. If the fulcrum is closer to the force being applied, the load can be moved a greater distance at the expense of requiring a greater input force. If the fulcrum is closer to the load, less force is required but the force must be applied over a longer distance. An example of a first-class lever is a seesaw / teeter-totter.

4 If A = 5 ft. and the green box weighs 45 lbs. what is the torque acting on the A side of this lever?

74% Answer Correctly

	675 ft⋅lb
	75 ft⋅lb
	225 ft⋅lb
	56 ft⋅lb

Solution

For a lever, torque is weight x distance from the fulcrum which, in this case, is: 45 ft. x 5 lbs. = 225 ft⋅lb

One Horsepower (hp) is equal to how many watts?

76% Answer Correctly

	9.8
	746
	1492
	1

Solution

Power is the rate at which work is done, P = w/t, or work per unit time. The watt (W) is the unit for power and is equal to 1 joule (or newton-meter) per second. Horsepower (hp) is another familiar unit of power used primarily for rating internal combustion engines. 1 hp equals 746 watts.