ASVAB Mechanical Comprehension Practice Test 820037 Results

	Your Results	Global Average
Questions	5	5
Correct	0	3.16
Score	0%	63%

Review

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?

63% Answer Correctly

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

Connected gears of different numbers of teeth are used together to change which of the following charasteristics of the input force?

65% Answer Correctly

	torque
	force
	rotational direction
	energy

Solution

Connected gears of different numbers of teeth are used together to change the rotational speed and torque of the input force. If the smaller gear drives the larger gear, the speed of rotation will be reduced and the torque will increase. If the larger gear drives the smaller gear, the speed of rotation will increase and the torque will be reduced.

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
	0.83 lbs
	45 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

The standard unit of energy is the:

73% Answer Correctly

	Volt
	Horsepower
	Joule
	Watt

Solution

The Joule (J) is the standard unit of energy and has the unit \({kg \times m^2} \over s^2\).

5 The green box weighs 40 lbs. and a 35 lbs. weight is placed 1 ft. from the fulcrum at the blue arrow. How far from the fulcrum would the green box need to be placed to balance the lever?

57% Answer Correctly

	0.88 ft.
	0.44 ft.
	1.75 ft.
	2.63 ft.

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 d_a, our missing value, and plugging in our variables yields:

d_a = \( \frac{R_bd_b}{R_a} \) = \( \frac{35 lbs. \times 1 ft.}{40 lbs.} \) = \( \frac{35 ft⋅lb}{40 lbs.} \) = 0.88 ft.