ASVAB Mechanical Comprehension Practice Test 470926 Results

	Your Results	Global Average
Questions	5	5
Correct	0	3.32
Score	0%	66%

Review

Specific gravity is a comparison of the density of an object with the density of:

57% Answer Correctly

	oil
	carbon
	water
	air

Solution

Specific gravity is the ratio of the density of equal volumes of a substance and water and is measured by a hyrdometer.

2 10 lbs. of effort is used by a machine to lift a 60 lbs. box. What is the mechanical advantage of the machine?

84% Answer Correctly

	6
	2
	15
	7.5

Solution

Mechanical advantage is resistance force divided by effort force:

MA = \( \frac{F_r}{F_e} \) = \( \frac{60 lbs.}{10 lbs.} \) = 6

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

	45 lbs
	810 lbs
	90 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

4 If the green box weighs 15 lbs. and is 1 ft. from the fulcrum, how far from the fulcrum would a 75 lbs. force need to be applied to balance the lever?

58% Answer Correctly

	0 ft.
	0.2 ft.
	0.07 ft.
	0.6 ft.

Solution

To balance this lever the torques at the green box and the blue arrow 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 green box and b the blue arrow, R is resistance (weight/force) and d is the distance from the fulcrum.

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

d_b = \( \frac{R_ad_a}{R_b} \) = \( \frac{15 lbs. \times 1 ft.}{75 lbs.} \) = \( \frac{15 ft⋅lb}{75 lbs.} \) = 0.2 ft.

The force required to initally get an object moving is __________ the force required to keep it moving.

76% Answer Correctly

	higher than
	lower than
	the same as
	opposite

Solution

For any given surface, the coefficient of static friction is higher than the coefficient of kinetic friction. More force is required to initally get an object moving than is required to keep it moving. Additionally, static friction only arises in response to an attempt to move an object (overcome the normal force between it and the surface).